Media Player problem - bizarre!

I've been running dual monitors on a Matrox G450 dual-head for years
under NT4. I recently upgraded to XP Pro SP2. I continued to run a
"stretched" desktop (2048 x 768) after the upgrade.

Now I can only view video in Media Player on the primary monitor. If
Media Player is on the second monitor, the video pane remains blank
while the movie plays. If I drag Media Player to the primary monitor,
the video appears as the window is dragged - drag it back and it goes
blank again. If I split Media Player across monitors, the portion on the
primary monitor displays video while the other half remains blank.

This behavior certainly qualifies as one of the more bizarre Windows
issues I have encountered ;-) Any suggestions?

TIA

Sunny