QWizard is acting strange.

Creating a QWizard with parent of my MainWindow in my application resulted in following bug:

When I click "New", the MainWindow's title removes itself, parts of the window boders also removed theirselves. The window never recovers. Looks like the Aero extended itself into the MainWindow somehow... In the console, a bunch of:
nativeResourceForWindow: 'handle' requested for null window or window without handle.
appears. My MainWindow is corrupted.

Tried to make small sample but the bug didnt reproduces. However, in my real application, it always happens.