Menu unusable after switching screen

The following steps might only reproduce the issue on my machine. If you tell me where to add lines for printing debugging output, I'll run them for you.

1. Open a file in Creator.
2. Maximize Creator on primary screen.
3. Switch off primary screen.
   Everything on the primary screen will be moved to the secondary screen. This includes open Windows like Creator's, Windows Taskbar and Desktop symbols. During this, everything will be resized because the secondary screen's scaling is only 100%.
4. Switch on primary screen again.
   Everything will be moved back to the primary screen.
5. Click on Creator's menu bar.
   Creator will now do any of the following:
   • display the menu correctly
   • not display the menu at all
   • display the menu much to small: screenshot
   • trigger an unrelated UI element, e.g. the file selection combo box.

I could not yet reproduce this with a simpler Qt example project.

Creator should be able to handle the switching of screens.