I had a similar problem with mpc and wmp on an older, flakey video card above certain resolutions. It annoyed me to no end. Video card driver updates changed the shape and size of the torn box though.

It was one of the reasons that when that card completely flaked (catastrophic memory failure), I bought an ati card. My last 2 nvidia cards behaved similarly. The ATI card doesn't, but it's buggy differently.

I don't know what to tell you exactly, other than I've seen the same behavior myself and it may be related to how your video card interacts with the rest of your system (including opengl layers and whatnot).