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[coco8] BUG: strange error report in Xcode backup console (iOS 9.3)

The Xcode debug console reported an error situation where they are not triggering an exception.
The system did not crash but we canīt warty it is stable at VM level.

Symptom

The error happens when we was downloading a file and opened an Alert box after the download complete.
See FileDownload>>#example

Reproducible?

The error was NOT reported all times we run the test.

Dump of error

2016-04-10 15:58:06.673 coco8[795:360387] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
 Stack:(
	0   CoreFoundation                      0x00000001825eee50 <redacted> + 148
	1   libobjc.A.dylib                     0x0000000181c53f80 objc_exception_throw + 56
	2   CoreFoundation                      0x00000001825eed80 <redacted> + 0
	3   Foundation                          0x000000018309fafc <redacted> + 88
	4   Foundation                          0x0000000182f20ccc <redacted> + 36
	5   UIKit                               0x0000000187fcb7c0 <redacted> + 912
	6   UIKit                               0x0000000187fccd38 <redacted> + 788
	7   UIKit                               0x0000000187fcc96c <redacted> + 296
	8   UIKit                               0x000000018809c3b8 <redacted> + 480
	9   UIKit                               0x0000000188099380 <redacted> + 172
	10  UIKit                               0x00000001880995f0 <redacted> + 96
	11  UIKit                               0x0000000188099ab4 <redacted> + 80
	12  UIKit                               0x000000018809e080 <redacted> + 492
	13  UIKit                               0x000000018809d1ec <redacted> + 148
	14  UIKit                               0x000000018809d12c <redacted> + 284
	15  UIKit                               0x0000000187badf90 <redacted> + 444
	16  UIKit                               0x0000000187bae064 <redacted> + 60
	17  UIKit                               0x0000000187bae1a4 <redacted> + 28
	18  UIKit                               0x0000000187bad754 <redacted> + 100
	19  UIKit                               0x0000000187738b40 <redacted> + 996
	20  UIKit                               0x0000000187738744 <redacted> + 28
	21  UIKit                               0x0000000187ac0138 <redacted> + 108
	22  UIKit                               0x0000000187ab92c8 <redacted> + 1328
	23  UIKit                               0x0000000187abad64 <redacted> + 4644
	24  UIKit                               0x0000000187abd7a0 <redacted> + 472
	25  UIKit                               0x00000001878332b4 <redacted> + 184
	26  UIKit                               0x000000018808a5c4 <redacted> + 512
	27  UIKit                               0x0000000188088b78 <redacted> + 228
	28  UIKit                               0x0000000187bbe534 <redacted> + 260
	29  coco8                               0x00000001000e20a8 ffi_call_SYSV + 100
	30  coco8                               0x00000001000e0738 ffi_call + 176
	31  coco8                               0x0000000100096e5c jsCocoaObject_getProperty + 4624
	32  JavaScriptCore                      0x000000018603eb5c <redacted> + 324
	33  JavaScriptCore                      0x0000000185ca693c <redacted> + 1248
	34  JavaScriptCore                      0x00000001860ea7c0 <redacted> + 9936
	35  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	36  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	37  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	38  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	39  JavaScriptCore                      0x00000001860edf14 <redacted> + 24100
	40  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	41  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	42  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	43  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	44  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	45  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	46  JavaScriptCore                      0x00000001860e7ed8 <redacted> + 312
	47  JavaScriptCore                      0x00000001860139fc <redacted> + 180
	48  JavaScriptCore                      0x0000000185cb266c <redacted> + 400
	49  JavaScriptCore                      0x0000000185cb241c JSObjectCallAsFunction + 520
	50  coco8                               0x00000001000c26b8 +[BurksPool callSelector:ofInstance:writeContext:withArguments:] + 1328
	51  coco8                               0x00000001000c0f0c -[BurksPool v_id:id:id:] + 128
	52  CFNetwork                           0x0000000182cfdbac <redacted> + 36
	53  Foundation                          0x0000000182fa8510 <redacted> + 16
	54  Foundation                          0x0000000182efa900 <redacted> + 96
	55  Foundation                          0x0000000182eeaed8 <redacted> + 604
	56  Foundation                          0x0000000182faa904 <redacted> + 224
	57  libdispatch.dylib                   0x00000001001c5a3c _dispatch_client_callout + 16
	58  libdispatch.dylib                   0x00000001001d2554 _dispatch_queue_drain + 1036
	59  libdispatch.dylib                   0x00000001001c972c _dispatch_queue_invoke + 464
	60  libdispatch.dylib                   0x00000001001d466c _dispatch_root_queue_drain + 760
	61  libdispatch.dylib                   0x00000001001d4364 _dispatch_worker_thread3 + 132
	62  libsystem_pthread.dylib             0x0000000182251470 _pthread_wqthread + 1092
	63  libsystem_pthread.dylib             0x0000000182251020 start_wqthread + 4
)
2016-04-10 15:58:06.694 coco8[795:360387] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
 Stack:(
	0   CoreFoundation                      0x00000001825eee50 <redacted> + 148
	1   libobjc.A.dylib                     0x0000000181c53f80 objc_exception_throw + 56
	2   CoreFoundation                      0x00000001825eed80 <redacted> + 0
	3   Foundation                          0x000000018309fafc <redacted> + 88
	4   Foundation                          0x000000018309f9c0 <redacted> + 56
	5   Foundation                          0x0000000182f251ec <redacted> + 56
	6   Foundation                          0x0000000182f20dac <redacted> + 260
	7   UIKit                               0x0000000187fcb7c0 <redacted> + 912
	8   UIKit                               0x0000000187fccd38 <redacted> + 788
	9   UIKit                               0x0000000187fcc96c <redacted> + 296
	10  UIKit                               0x000000018809c3b8 <redacted> + 480
	11  UIKit                               0x0000000188099380 <redacted> + 172
	12  UIKit                               0x00000001880995f0 <redacted> + 96
	13  UIKit                               0x0000000188099ab4 <redacted> + 80
	14  UIKit                               0x000000018809e080 <redacted> + 492
	15  UIKit                               0x000000018809d1ec <redacted> + 148
	16  UIKit                               0x000000018809d12c <redacted> + 284
	17  UIKit                               0x0000000187badf90 <redacted> + 444
	18  UIKit                               0x0000000187bae064 <redacted> + 60
	19  UIKit                               0x0000000187bae1a4 <redacted> + 28
	20  UIKit                               0x0000000187bad754 <redacted> + 100
	21  UIKit                               0x0000000187738b40 <redacted> + 996
	22  UIKit                               0x0000000187738744 <redacted> + 28
	23  UIKit                               0x0000000187ac0138 <redacted> + 108
	24  UIKit                               0x0000000187ab92c8 <redacted> + 1328
	25  UIKit                               0x0000000187abad64 <redacted> + 4644
	26  UIKit                               0x0000000187abd7a0 <redacted> + 472
	27  UIKit                               0x00000001878332b4 <redacted> + 184
	28  UIKit                               0x000000018808a5c4 <redacted> + 512
	29  UIKit                               0x0000000188088b78 <redacted> + 228
	30  UIKit                               0x0000000187bbe534 <redacted> + 260
	31  coco8                               0x00000001000e20a8 ffi_call_SYSV + 100
	32  coco8                               0x00000001000e0738 ffi_call + 176
	33  coco8                               0x0000000100096e5c jsCocoaObject_getProperty + 4624
	34  JavaScriptCore                      0x000000018603eb5c <redacted> + 324
	35  JavaScriptCore                      0x0000000185ca693c <redacted> + 1248
	36  JavaScriptCore                      0x00000001860ea7c0 <redacted> + 9936
	37  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	38  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	39  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	40  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	41  JavaScriptCore                      0x00000001860edf14 <redacted> + 24100
	42  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	43  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	44  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	45  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	46  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	47  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	48  JavaScriptCore                      0x00000001860e7ed8 <redacted> + 312
	49  JavaScriptCore                      0x00000001860139fc <redacted> + 180
	50  JavaScriptCore                      0x0000000185cb266c <redacted> + 400
	51  JavaScriptCore                      0x0000000185cb241c JSObjectCallAsFunction + 520
	52  coco8                               0x00000001000c26b8 +[BurksPool callSelector:ofInstance:writeContext:withArguments:] + 1328
	53  coco8                               0x00000001000c0f0c -[BurksPool v_id:id:id:] + 128
	54  CFNetwork                           0x0000000182cfdbac <redacted> + 36
	55  Foundation                          0x0000000182fa8510 <redacted> + 16
	56  Foundation                          0x0000000182efa900 <redacted> + 96
	57  Foundation                          0x0000000182eeaed8 <redacted> + 604
	58  Foundation                          0x0000000182faa904 <redacted> + 224
	59  libdispatch.dylib                   0x00000001001c5a3c _dispatch_client_callout + 16
	60  libdispatch.dylib                   0x00000001001d2554 _dispatch_queue_drain + 1036
	61  libdispatch.dylib                   0x00000001001c972c _dispatch_queue_invoke + 464
	62  libdispatch.dylib                   0x00000001001d466c _dispatch_root_queue_drain + 760
	63  libdispatch.dylib                   0x00000001001d4364 _dispatch_worker_thread3 + 132
	64  libsystem_pthread.dylib             0x0000000182251470 _pthread_wqthread + 1092
	65  libsystem_pthread.dylib             0x0000000182251020 start_wqthread + 4
)
2016-04-10 15:58:06.708 coco8[795:360387] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
 Stack:(
	0   CoreFoundation                      0x00000001825eee50 <redacted> + 148
	1   libobjc.A.dylib                     0x0000000181c53f80 objc_exception_throw + 56
	2   CoreFoundation                      0x00000001825eed80 <redacted> + 0
	3   Foundation                          0x000000018309fafc <redacted> + 88
	4   Foundation                          0x0000000182f20ccc <redacted> + 36
	5   UIKit                               0x0000000187fcb810 <redacted> + 992
	6   UIKit                               0x0000000187fccd38 <redacted> + 788
	7   UIKit                               0x0000000187fcc96c <redacted> + 296
	8   UIKit                               0x000000018809c3b8 <redacted> + 480
	9   UIKit                               0x0000000188099380 <redacted> + 172
	10  UIKit                               0x00000001880995f0 <redacted> + 96
	11  UIKit                               0x0000000188099ab4 <redacted> + 80
	12  UIKit                               0x000000018809e080 <redacted> + 492
	13  UIKit                               0x000000018809d1ec <redacted> + 148
	14  UIKit                               0x000000018809d12c <redacted> + 284
	15  UIKit                               0x0000000187badf90 <redacted> + 444
	16  UIKit                               0x0000000187bae064 <redacted> + 60
	17  UIKit                               0x0000000187bae1a4 <redacted> + 28
	18  UIKit                               0x0000000187bad754 <redacted> + 100
	19  UIKit                               0x0000000187738b40 <redacted> + 996
	20  UIKit                               0x0000000187738744 <redacted> + 28
	21  UIKit                               0x0000000187ac0138 <redacted> + 108
	22  UIKit                               0x0000000187ab92c8 <redacted> + 1328
	23  UIKit                               0x0000000187abad64 <redacted> + 4644
	24  UIKit                               0x0000000187abd7a0 <redacted> + 472
	25  UIKit                               0x00000001878332b4 <redacted> + 184
	26  UIKit                               0x000000018808a5c4 <redacted> + 512
	27  UIKit                               0x0000000188088b78 <redacted> + 228
	28  UIKit                               0x0000000187bbe534 <redacted> + 260
	29  coco8                               0x00000001000e20a8 ffi_call_SYSV + 100
	30  coco8                               0x00000001000e0738 ffi_call + 176
	31  coco8                               0x0000000100096e5c jsCocoaObject_getProperty + 4624
	32  JavaScriptCore                      0x000000018603eb5c <redacted> + 324
	33  JavaScriptCore                      0x0000000185ca693c <redacted> + 1248
	34  JavaScriptCore                      0x00000001860ea7c0 <redacted> + 9936
	35  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	36  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	37  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	38  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	39  JavaScriptCore                      0x00000001860edf14 <redacted> + 24100
	40  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	41  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	42  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	43  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	44  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	45  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	46  JavaScriptCore                      0x00000001860e7ed8 <redacted> + 312
	47  JavaScriptCore                      0x00000001860139fc <redacted> + 180
	48  JavaScriptCore                      0x0000000185cb266c <redacted> + 400
	49  JavaScriptCore                      0x0000000185cb241c JSObjectCallAsFunction + 520
	50  coco8                               0x00000001000c26b8 +[BurksPool callSelector:ofInstance:writeContext:withArguments:] + 1328
	51  coco8                               0x00000001000c0f0c -[BurksPool v_id:id:id:] + 128
	52  CFNetwork                           0x0000000182cfdbac <redacted> + 36
	53  Foundation                          0x0000000182fa8510 <redacted> + 16
	54  Foundation                          0x0000000182efa900 <redacted> + 96
	55  Foundation                          0x0000000182eeaed8 <redacted> + 604
	56  Foundation                          0x0000000182faa904 <redacted> + 224
	57  libdispatch.dylib                   0x00000001001c5a3c _dispatch_client_callout + 16
	58  libdispatch.dylib                   0x00000001001d2554 _dispatch_queue_drain + 1036
	59  libdispatch.dylib                   0x00000001001c972c _dispatch_queue_invoke + 464
	60  libdispatch.dylib                   0x00000001001d466c _dispatch_root_queue_drain + 760
	61  libdispatch.dylib                   0x00000001001d4364 _dispatch_worker_thread3 + 132
	62  libsystem_pthread.dylib             0x0000000182251470 _pthread_wqthread + 1092
	63  libsystem_pthread.dylib             0x0000000182251020 start_wqthread + 4
)
2016-04-10 15:58:06.719 coco8[795:360387] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
 Stack:(
	0   CoreFoundation                      0x00000001825eee50 <redacted> + 148
	1   libobjc.A.dylib                     0x0000000181c53f80 objc_exception_throw + 56
	2   CoreFoundation                      0x00000001825eed80 <redacted> + 0
	3   Foundation                          0x000000018309fafc <redacted> + 88
	4   Foundation                          0x000000018309f9c0 <redacted> + 56
	5   Foundation                          0x0000000182f251ec <redacted> + 56
	6   Foundation                          0x0000000182f20dac <redacted> + 260
	7   UIKit                               0x0000000187fcb810 <redacted> + 992
	8   UIKit                               0x0000000187fccd38 <redacted> + 788
	9   UIKit                               0x0000000187fcc96c <redacted> + 296
	10  UIKit                               0x000000018809c3b8 <redacted> + 480
	11  UIKit                               0x0000000188099380 <redacted> + 172
	12  UIKit                               0x00000001880995f0 <redacted> + 96
	13  UIKit                               0x0000000188099ab4 <redacted> + 80
	14  UIKit                               0x000000018809e080 <redacted> + 492
	15  UIKit                               0x000000018809d1ec <redacted> + 148
	16  UIKit                               0x000000018809d12c <redacted> + 284
	17  UIKit                               0x0000000187badf90 <redacted> + 444
	18  UIKit                               0x0000000187bae064 <redacted> + 60
	19  UIKit                               0x0000000187bae1a4 <redacted> + 28
	20  UIKit                               0x0000000187bad754 <redacted> + 100
	21  UIKit                               0x0000000187738b40 <redacted> + 996
	22  UIKit                               0x0000000187738744 <redacted> + 28
	23  UIKit                               0x0000000187ac0138 <redacted> + 108
	24  UIKit                               0x0000000187ab92c8 <redacted> + 1328
	25  UIKit                               0x0000000187abad64 <redacted> + 4644
	26  UIKit                               0x0000000187abd7a0 <redacted> + 472
	27  UIKit                               0x00000001878332b4 <redacted> + 184
	28  UIKit                               0x000000018808a5c4 <redacted> + 512
	29  UIKit                               0x0000000188088b78 <redacted> + 228
	30  UIKit                               0x0000000187bbe534 <redacted> + 260
	31  coco8                               0x00000001000e20a8 ffi_call_SYSV + 100
	32  coco8                               0x00000001000e0738 ffi_call + 176
	33  coco8                               0x0000000100096e5c jsCocoaObject_getProperty + 4624
	34  JavaScriptCore                      0x000000018603eb5c <redacted> + 324
	35  JavaScriptCore                      0x0000000185ca693c <redacted> + 1248
	36  JavaScriptCore                      0x00000001860ea7c0 <redacted> + 9936
	37  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	38  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	39  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	40  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	41  JavaScriptCore                      0x00000001860edf14 <redacted> + 24100
	42  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	43  JavaScriptCore                      0x00000001860edce0 <redacted> + 23536
	44  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	45  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	46  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	47  JavaScriptCore                      0x00000001860edd44 <redacted> + 23636
	48  JavaScriptCore                      0x00000001860e7ed8 <redacted> + 312
	49  JavaScriptCore                      0x00000001860139fc <redacted> + 180
	50  JavaScriptCore                      0x0000000185cb266c <redacted> + 400
	51  JavaScriptCore                      0x0000000185cb241c JSObjectCallAsFunction + 520
	52  coco8                               0x00000001000c26b8 +[BurksPool callSelector:ofInstance:writeContext:withArguments:] + 1328
	53  coco8                               0x00000001000c0f0c -[BurksPool v_id:id:id:] + 128
	54  CFNetwork                           0x0000000182cfdbac <redacted> + 36
	55  Foundation                          0x0000000182fa8510 <redacted> + 16
	56  Foundation                          0x0000000182efa900 <redacted> + 96
	57  Foundation                          0x0000000182eeaed8 <redacted> + 604
	58  Foundation                          0x0000000182faa904 <redacted> + 224
	59  libdispatch.dylib                   0x00000001001c5a3c _dispatch_client_callout + 16
	60  libdispatch.dylib                   0x00000001001d2554 _dispatch_queue_drain + 1036
	61  libdispatch.dylib                   0x00000001001c972c _dispatch_queue_invoke + 464
	62  libdispatch.dylib                   0x00000001001d466c _dispatch_root_queue_drain + 760
	63  libdispatch.dylib                   0x00000001001d4364 _dispatch_worker_thread3 + 132
	64  libsystem_pthread.dylib             0x0000000182251470 _pthread_wqthread + 1092
	65  libsystem_pthread.dylib             0x0000000182251020 start_wqthread + 4
)