I've noticed a problem with Windows Media Player 10 (unsure if 9, 8,
or 7 were any different).  If I play several media files in a
playlist, the first file will look fine but all the ones after will be
slightly brighter and washed out.  I can see the difference
immediately as the first file changes to the next.

I've found a workaround that will restore the current file to normal
is to close it (File->Close or Ctrl+W) and then start playing it again
with Ctrl+P.  The file will then play fine, but unfortunately the next
file will be too bright and washed out again.  It is tedious to keep
repeating this process for every file, and it partially defeats the
purposing of using a playlist.

I've seen this with .mpg and .avi (DivX) files, but .wmv files seem
okay.

This is a reproducible bug.  Is there some procedure for submitting
bug reports to Microsoft?