showFullcreen on multi monitor systems always shows the window fullscreen on the primary monitor.

When I call showFullscreen on a window I expect it to be shown fullscreen on the monitor the window is located. This was the behaviour on Qt 4.8.2 when setting the Qt::WindowFullScreen flag on the window state. Now, if I call showFullscreen on a window in Qt 5.0.2, that window gets shown in fullscreen mode, however, always on the primary monitor, not on the monitor the window is located.

What I found is that previously (Qt 4.8.2) the geomtry used to position the window in fullscreen mode got fetched via 'QApplication::desktop()>screenNumber(pWindow)', in Qt 5.0.2 the geometry gets fetched via 'pWindow>window()>windowHandle()>screen()->geometry()'. The latter seems to ALWAYS return the geometry of the primary screen no matter where the window is located on the desktop.

This 'new' behaviour is especially problematic in my situation because I have several graphic views which shall be shown fullscreen on different screens on multi head systems (two or more monitors).

Note: Attached is a small test project which I created to test this issue.