Problems using Qt widgets in a Cocoa application

I have troubles in the following scenario:
There is a Cocoa (Mac OS) application running its own event loop and I am using QWidgets within it. I do not need to insert QWidgets into Cocoa view hierarchy, they are only used independently. I am instantiating a QApplication on the main application thread before any widget, but not executing its event loop. AA_MacPluginApplication attribute is set on QApplication before instantiating it.

The troubles I met so far:

# The application becomes unresponsive after a QDialog is closed (whether accepted or not).
# The same happens when an item in a QComboBox is clicked.
# A segmentation fault occurs when scrolling a QListWidget on a touchpad using 2-finger scrolling technique (but not when using scrollbar). Gdb backtrace: http://pastebin.com/tGFC1C1X

What might be the reasons and how to remedy this?