maybe not MB are creating these thumbnails. try to uninstall WMP. WMP can do weird things even in background.
From the filename structure of those thumbnails, I guess they are located
- in MusicBee\AppData\InternalCache\AlbumCovers (Portable version)
- or in %LOCALAPPDATA%\MusicBee\InternalCache\AlbumCovers (Installed version)
There are no similar duplicates on my computer, except when using the 'Rounded Artwork' plugin (=> at most 1 duplicate).
But in my collection, album covers are stored only once per album, as cover.jpg/png in the respective folder,
and I systematically remove the pictures embedded in the audio files.
@LedHarvest:
When you have duplicates, is the album artwork embedded in the matching audio files?
That's just an assumption to explain the redundancy.