libqcocoa QNSWindowHelper handleWindowEvent crash in popup dialog

I'm getting a crash (stack trace below) just when Dialog windows appear – it is not 100% reliable – more like 50%. Perhaps has something to do with mouse movement as window is appearing. Only happens in 5.3.0 – I just reverted back to 5.2.0 and was unable to reproduce it. A Dialog with a TreeView is particularly susceptible it seems – I'll do some more testing and try to narrow it down, and include a test case, when I get a chance a bit later.

• thread #1: tid = 0x429737, 0x0000000105c73091 libobjc.A.dylib`objc_msgSend + 17, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
• frame #0: 0x0000000105c73091 libobjc.A.dylib`objc_msgSend + 17
  frame #1: 0x000000011450d689 libqcocoa.dylib`-[QNSWindowHelper handleWindowEvent:] + 153
  frame #2: 0x000000010da2b5d4 AppKit`-[NSApplication sendEvent:] + 2021
  frame #3: 0x000000011452309e libqcocoa.dylib`-[QNSApplication sendEvent:] + 78
  frame #4: 0x000000010d87ba19 AppKit`-[NSApplication run] + 646
  frame #5: 0x000000011451f854 libqcocoa.dylib`QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 2404
  frame #6: 0x0000000101c2c93d QtCore`QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 381
  frame #7: 0x0000000101c2fe77 QtCore`QCoreApplication::exec() + 359

A similar stack trace is found in these other bugs, which may or may not be related:

• https://bugreports.qt-project.org/browse/QTBUG-36045
• https://bugreports.qt-project.org/browse/QTBUG-35257