I get a crash on OSX hard to reproduce and the stack trace doesn't really help me

Sometimes the UI get stuck and it crashes. I have a few dialogs showing up but nothing specific. It used to work with 4.6.3 (carbon).
Now I switched to 4.8.0 (cocoa).

the stack trace:
#0 0x00007fff86adcf10 in objc_msgSend ()
#1 0x00007fff859c559e in -[NSWindow _verifyDefaultButtonCell:] ()
#2 0x00007fff85a849e3 in -[NSView _displayRectIgnoringOpacity:isVisibleRect:rectIsVisibleRectForView:] ()
#3 0x00007fff859fec0e in -[NSView displayIfNeeded] ()
#4 0x00007fff859f9aba in _handleWindowNeedsDisplay ()
#5 0x00007fff8840ebc5 in __NSFireTimer ()
#6 0x00007fff805e4bb8 in __CFRunLoopRun ()
#7 0x00007fff805e2d8f in CFRunLoopRunSpecific ()
#8 0x00007fff8865974e in RunCurrentEventLoopInMode ()
#9 0x00007fff886594b1 in ReceiveNextEventCommon ()
#10 0x00007fff8865940c in BlockUntilNextEventMatchingListInMode ()
#11 0x00007fff859ceeb2 in _DPSNextEvent ()
#12 0x00007fff859ce801 in -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] ()
#13 0x00007fff8599468f in -[NSApplication run] ()
#14 0x0000000101e11220 in QEventDispatcherMac::processEvents ()
#15 0x0000000102b4b894 in QEventLoop::processEvents ()
#16 0x0000000102b4bc47 in QEventLoop::exec ()
#17 0x0000000102b4feba in QCoreApplication::exec ()
#18 0x0000000100006a7e in main (argc=1, argv=0x7fff5fbff550) at main.cpp:48

It looks like there is message sent to a deleted widget.