Using Windows 7 system with an external monitor connected as an extended screen.
Qt application uses mainwindow class derived from QWidget which has 'Always on Top' window flag set.

When the external monitor is detached:

1) If the window was placed on the secondary screen before the monitor is detached, the window disappears/minimized and is not possible to get back the window to be shown, the application is visible in system tray but cannot show the window anymore.

2)If the window was placed on the primary screen before the monitor is detached, then then window appears on the screen but the window has lost its always on top flag and re-setting the flag does not have any affect on the window behavior, also the windowFrameIconClicked() signal is not emitted anymore, not sure what causes this to happen.

These issues are not seen in Qt 4.8, reproducible with 5.3.0 Beta and Qt 5.2.1 on Windows 7 platform.