this issue started (for me) with the new builds starting from last month. I manually edit the info/art of each individual song, so the songs I started editing after installing the faulty build were affected by this problem. The art displayed fine on MM, but in the Windows 7 file explorer, it would have a distorted thumbnail, with different colors than the original album art. Even weirder, it wouldn't display on my Android device entirely (the art, not the .mp3 file) When I tried putting my music onto my Cowon D2, selecting the song would cause it to freeze up. I'm pretty sure that it has to do with the new build, because the rest of my library edited before the build installed (and mp3 files downloaded with album art included) display perfectly fine on my D2, Android device, and Windows Explorer.
Sorry that i can't be more specific about which build this problem began with.
Below is a screenshot showing the problem