flickering lines while playing xvid

hi

ive had a problem for a while now. Since ive bought a Matrox P650 card i 
get some kind of overlay problem when playing some xvid files.  The 1-2 
top lines flickers during playback if black bars is in video its just 
below the top black bar.

it only appears in some xvid-videofiles. not all.

i can see difference when i check one of theese (from matrox powerdesk 
util) and try to play the same file. But if one of them works others 
dont. I even got the computer to hang when using..hmm think it was YUY2
Video Surface - force pitch to width YV12
Video Surface - force pitch to width YUY2

windows xp sp2
matrox p650 pci-e (ive tried the 3 latest drivers with no luck)
mplayer orc1 with codecpack (i use vo=directx)

re Matte