Disable Screen Saver during Media Player via GPO

I currently have a GPO that forces a password protected screen saver on all
users in my domain after 5 minutes. However, if they are watching a video in
Windows Media Player I want to disable the screen saver. In the same GPO I
disabled "Allow Screen Saver" under /Users/Windows Componets/Windows Media
Player/Playback.

According to the description "When this policy is disabled, a screen saver
does not interrupt playback even if users have selected a screen saver. The
Allow screen saver during playback check box is cleared and is not available."

I have verified that the check box is cleared and is not available, but the
screen saver still comes on during playback.

All computers are running XP Pro SP2 with Windows Media Player 11.

Thanks in advance.