This is a bug/feature in Windows Media Player for which I can't find a workaround or fix aside from watching the movie on the secondary screen or using a different media player. VLC Media Player
does not exhibit this behavior in full screen mode. Changing the taskbar's behavior so that it hides itself when not in use does alleviate the problem, but not entirely.
Edited by Andrew, 15 June 2011 - 03:16 AM.