That's correct and surely enabled for Helios61There is an option in the mp configuration in music -> music database
"Use existing album art to:" ... (checkbox) create artist preview thumbs
I guess this checkbox is set in your configuration.
Maybe you have to delete the already created thumbs in the thumbs/artists folder manually.
I don´t know why this feature is in there. Personally I don´t see the need, I do want the artist thumbs but not these tile thumbs. But someone must have had a reason to put this option there.
(and you'll definately connect a known album cover to an artist) than reading text.