This may be a bug in the way windows dispalys things, or maybe with my graphics card or something, but since the only application I have that uses transparencies is Plus, I can't really test it, so I thought I'd post here.

If you resize a transparent window either up or to the left (or both) then the background moves with it. See attachment for example (I moved the contact list after the resizing.)

Sorry if this is a known bug or just a problem with Windows itslef, I didn't find it in my searching. I never noticed it with Plus 3.6 and MSN 7.5, but I never used transparency much.