If you're trying to do multiple artists and change the display artist *before* opening the multiple artist splitter, it reverts to the original display artist and you have to do it all over again. Could it prompt to save the new display artist or something so that we don't have to close out the tag editor and reopen it to continue?
Added: Okay, one more item. Could there be some way to quickly tell what role you have an artist assigned to? I just want to see that I have Performer, Guest Artist, Remixer assigned correctly without going through several clicks. Maybe a tooltip like genre? Even if you had to open the Edit screen to access it, it would be easier than the current situation.