Maximized ribbon window position issue on Windows 7 when the OS taskbar is docked to the left

When the OS taskbar is docked to the left and the ribbon window is maximized, the ribbon window does not use the whole area of the screen, instead it leaves a gap between the taskbar and the left border of the window and the right border of the window is cut out.

It seems that the issue only occurs on windows 7 and the same test app works fine on my Windows 8 dev PC.

Any help appreciated.

Roger