Disable taskbar lock?

When I open a window that is maximized, sometimes the taskbar locks and a white line appears, and I can't open the taskbar unless I press the windows key. How do I stop this?

(If you cant see the line open it in new tab)

Fabler2 said:

That's a bug. Taskbar opens but behind the max window. It only happens now and again. Got fed up of it so disabled automatically hide the taskbar in desktop mode.

For me half the time I open a maximized window this happens