Main Window Menu Bar background not filling entire width when form shown as Maximized

If a main window with a menu bar is shown via showmaximized(), the menu bar background is only drawn up to a width that appears to match the size of the window as it was last saved in qt designer. If you then shrink the window using the restore down button in the upper right corner followed by maximizing it again via the maximize button in the upper right corner the menu bar background is now drawn correctly. It is very noticeable if you make the default window color say blue or something. This did not happen in QT 4.6. with the MS compilier