What may cause a crash in apple background queue in release configuration only?

What may cause a crash in apple background queue in release configuration
only?

The application i'm currently debugging crashes only when it's built under
release configuration. And what is more surprising it crashes in apple
background queue. Take a look at this:
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000001, 0x000000000000defe
Crashed Thread: 9
and this:
Thread 9 name: Dispatch queue: com.apple.root.background-priority
Thread 9 Crashed:
0 CoreFoundation 0x340102be CFRelease + 18
1 CoreFoundation 0x340106fc CFRelease + 1104
2 libobjc.A.dylib 0x3bdb0484 (anonymous
namespace)::AutoreleasePoolPage::pop(void*) + 164
3 libdispatch.dylib 0x3c1cf9cc _dispatch_root_queue_drain
+ 360
4 libdispatch.dylib 0x3c1cfabc _dispatch_worker_thread2 + 80
5 libsystem_c.dylib 0x3c1ffa0e _pthread_wqthread + 358
6 libsystem_c.dylib 0x3c1ff8a0 start_wqthread + 4
Can anybody give me a hint? What may cause such a crash?