MessageBox hidden behind Splashscreen on OSX

When opening a message box while a QSplashscreen is displayed the message box appears behind the QSplashscreen on OSX.

The scenario is quite common if one needs to report something during program startup. The hidden message box has the nasty effect that the program is waiting for user input. But the user doesn't know it because he doesn't see the message box. For him, the program appears to hang.

Please find attached a minimal example project, which demonstrates the effect.

I've made the following observations:

• This effect does only happen on OSX, on Windows the message box appears correctly in front of the splash screen (not tested on Linux).
• I'm using QApplication::activeWindow() as a parent for the message box. On windows, the activeWindow is the QSplashscreen, while on OSX, the activeWindow is 0. Nevertheless, even if I explicitly set the splash as the parent on OSX, the message box stays behind the splash.

This is similar to https://bugreports.qt.io/browse/QTBUG-35169. I chose, to open a new issue to give a more concise description. There the main point seems to be that the message box seems to prevent an interaction with the splash screen (which I find ok for a modal dialog). My point is that the message box should always be in front of the splash screen.