BUG IN CLIENT OF LIBDISPATCH: dispatch_sync called on queue already owned by current thread

Hi,

We have a Video Player App, which seem to crash randomly when player is closed.

Crash Info:

crash_info_entry_0 : BUG IN CLIENT OF LIBDISPATCH: dispatch_sync called on queue already owned by current thread

Stack trace:

0  libdispatch.dylib              0x12dd0 __DISPATCH_WAIT_FOR_QUEUE__ + 484
1  libdispatch.dylib              0x12900 _dispatch_sync_f_slow + 144
2  MediaToolbox                   0x1f6374 FigCaptionRendererSessionSetPlayer + 68
3  MediaToolbox                   0x2a7b30 setPlayerDo + 184
4  libdispatch.dylib              0x3950 _dispatch_client_callout + 20
5  libdispatch.dylib              0x12a70 _dispatch_lane_barrier_sync_invoke_and_complete + 56
6  MediaToolbox                   0x2a7a6c -[FigSubtitleCALayer setPlayer:] + 64
7  AVFCore                        0x6e2c0 -[AVPlayer _removeLayer:videoLayer:closedCaptionLayer:subtitleLayer:interstitialLayer:] + 572
8  AVFCore                        0x30dc8 -[AVPlayerLayer dealloc] + 324
9  Foundation                     0x2cf78 NSKVODeallocate + 216
10 QuartzCore                     0x68c54 CA::Layer::free_transaction(CA::Transaction*) + 404
11 QuartzCore                     0x4f284 CA::Transaction::commit() + 952
12 MediaToolbox                   0x3375bc setBounds + 376
13 MediaToolbox                   0x200160 UpdateLayoutContext + 892
14 MediaToolbox                   0x1feda8 onCaptionInputDo + 212
15 libdispatch.dylib              0x3950 _dispatch_client_callout + 20
16 libdispatch.dylib              0xb0ac _dispatch_lane_serial_drain + 664
17 libdispatch.dylib              0xbc10 _dispatch_lane_invoke + 392
18 libdispatch.dylib              0x16318 _dispatch_workloop_worker_thread + 656
19 libsystem_pthread.dylib        0x11b0 _pthread_wqthread + 288
20 libsystem_pthread.dylib        0xf50 start_wqthread + 8