I see a themed desktop. That is, the desktop does not look stock. Frankly I've found those themes to break stuff like that.
Try creating a new user account on the PC then head back to stock.
I have this issue for a while now. Been updating graphics drivers but never seems to fix it. Once in while the windows don't refresh or something and whats left is a stale graphic. It goes away after another window moves over that area of screen.