When Picard is used to tag albums and the album entry on musicbrainz contains more than one image wich results in the same filename, ' (1)', ' (2)' and so on are appended to the fileames, even if the option to replace spaces with underscores is set.

I ran into this issue with the Cowboys from Hell album from Pantera, and the settings in the attachments.

Ideally the tag appended to avoid duplicate filenames should be customizable (personally I'd use '_alt1'), or at least the space should be converted to an underscore if the options is set.

edit: apparently this also happens with songs, e.g. with the The Wrong Side of Heaven and the Righteous Side of Hell album by Five Finger Death Punch, which contains 2 song variants for some tracks, where one features another artist.