Oh, I should've mentioned this: I deleted all those files including folder.jpg's. That was the first thing i did, actually.

Hey everyone, I just spent like 5 hours trying to do this, and it's driving me insane. Apparently, WMP 11 embeds album art in such a screwed-up way that no other application I've tried (dbpoweramp converter, mp3tags, MM script "Album art tagger", etc.) would remove it. Now comes the funny part ...