Creator loses contact to its dialogs

1. Start Creator with empty settings, e.g. using the parameter "-tcs".
2. Open one of Creator's non-modal dialogs and leave that open.
   One example is "Help" -> "About Qt Creator".
3. Use Alt+Tab to bring a different application into the foreground.
4. Use Alt+Tab to return to Creator.
   Both windows appear, Creator's main window and the dialog.
5. In Creator's main window, open the QML Profiler.
   You don't need to record any data, just show the Profiler itself.
   Because of QTCREATORBUG-29892, the main window disappear and appears again immediately. The dialog now hides behind other windows, though.
6. Move other windows away, so you can see both again, Creator's main window and the dialog.
7. Use Alt+Tab to bring a different application into the foreground.
8. Use Alt+Tab to return to Creator.
   Only Creator's main window appears. The dialog doesn't.
9. Move other windows away, so you can see both again, Creator's main window and the dialog.
10. Close Creator's main window.
    The dialog stays open, the process "qtcreator" keeps running.

Bringing Qt Creator into the foreground should also show the dialog. Closing the main window should close the dialog, too, and exit the process.