Wrong screen reported when starting not on the primary screen on Mac OSX.

Operation:
Fire up an app on the secondary screen (the one without the menu bar). Enquire the window handle for the screen.

Expected result:
The secondary screen returned.

Actual result:
The primary screen returned.

More info:
When starting the app on the secondary screen, the primary screen is incorrectly returned. After moving the app window onto the primary screen, still the primary screen is reported (now correctly). After moving the app window back onto the secondary screen, the secondary screen is finally correctly reported. See the attached app. Here the output from the app, interleaved with the commentary what was done in the test with the app window.
"Color LCD" is the primary screen (the one with the menu bar)
"DELL P2414H" is the secondary screen (the one without the menu bar)

// start the application on the secondary screen, expect "DELL P2414H", but the wrong screen is reported
screen = 0x7fdfb2e63d10: Color LCD
// move the application to the primary screen, expect "Color LCD", correct behaviour
screen = 0x7fdfb2e63d10: Color LCD
// move back to the secondary screen, epxect "DELL P2414H", correct behaviour
screen = 0x7fdfb2e32d10: DELL P2414H

As a very unpleasant consequence, screenChanged signal is not fired when moving between the screens the very first time, which makes our app miss this important change.

Note that the other way round (starting on the primary screen and shifting onto the secondary), works fine.