Incorrect window size on 2 Displays with different scaling.

With 2 displays set to the same resolution and different windows scaling factors, switching from second screen only to extended mode (windows p) will cause the app window size to scale incorrectly. Issue can be seen with with "address book" and "qt extras - flat" sample apps as well as Qt creator.

Steps to Reproduce

1. Set scaling on primary display to > 100%, set scaling on secondary display to 100%
2. Set displays to second only mode, have Qt app show on second display
3. Set displays to extend mode

Observe that once on the primary display, the app window size is larger than it should be, as if it was retaining the scaling from the non-scaled secondary display (see attachments, % indicate scaling of primary display).

Issue does not reproduce if scaling of both displays is the same.

Issue does not reproduce if resolutions of displays are set different.