Floating dock widgets don't minimize with mainwindow if they have been floating initially

This seems to be Linux and window manager specific issue. Can be reproduced at least with openbox and metacity.

If a dock widget was floating as a result of restoreState() call, it does not minimize when QMainWindow is minimized. Docking and floating the dock widget causes it to minimize with QMainWidget again.

To reproduce:

• float the dockwidget
• close and restart the application
• minimize main window

-> the dock widget remains on screen