i noticed two metadata issues with artists with special characters today that you might be affected by.
Artists with special characters seems to have changed the way they are stored in IBN\artists.
'? and the mysterons' was stored as ' and the mysterons' but is now stored as 'and the mysterons', i had to delete artist folders starting with space to get mb3 to reference/use the new location successfully (show an artist image)
another example '*NSYNC' was stored as ' NSYNC' but now 'NSYNC'.
AC/DC folder.jpg image wasnt showing in dashboard, i deleted its IBN\artists folder and rescanned and now its image is showing ok (albeit showing as name 'AC DC' in album artists view top level and 'AC/DC' in AC/DC view and as 'AC/DC' in artist view) - so it could be that special characters are now dealt with in a different way, and the old way is corrupting the new way. Anyways in all instances if i deleted the related ibn folders and rescanned MB3 sorted itself out.
If you havent manually maintained any of your music metadata it may just be easier to delete IBN\artists and rescan library to ensure everything is tip top.(after a backup)