Does not repaint properly in fullscreen mode with multiple monitors

Steps to reproduce

• Start QtCreator and switch it to fullscreen mode

• Switch to another application, usually thats the browser and is non-fullscreen

• connect the external display which has a larger screen size and is set to be the main display so all applications are being moved to that one

• Switch to the fullscreen QtCreator window (usually by using Gesture, but using Cmd+Tab has the same effect)

Expected behavior

The QtCreator window fills the whole content of the main display

Actual behavior

The window is rendered at about the same size as the laptop display has, the rest of the screen is black as shown in qtcreator_small.png The hidden menubar however appears only after moving to the top of the screen and the macos titlebar is also drawn right below the menubar and not on top of the actual IDE contents as shown in qtcreator_small_menubar.png.

This worked fine with QtCreator 4.4, I didn't test 4.5 so far as I just upgraded to 4.6.1.