Are they actually embedded in the file (when you hover over them in the tag editor, the it says they're embedded) or are they just shown for the track?
If you artwork preferences include things like cover.jpg and folder.jpg and your music files are not organized and there are multiple instances of art in the folder where your music files are, all of them will be displayed for the tracks in that folder if you preferences allow for it.
Check for stray art where your music files are. If they exist, delete them or adjust your artwork preferences so MB ignores them.