The tag editor feature seems buggy when working with artist fields that have multiple values. When I try to set multiple artists on wma lossless files, either by using the "\\" trick or by adding an ARTIST field multiple times in extended tag editor, I get duplicate values and other problems. (For instance: Brahms\\CSO\\Perlman\\CSO\\Brahms). I've tried various ways to correct it, but none of the corrections "take." Possibly it was not designed to edit tags that have multiple values.
--I can edit these values successfully using the wmp 11 built-in tag editor, but perhaps this is not well documented for wma files.