I posted this on another forum, but it seems more appropriate here because it looks like an actual bug. It is related to some issues people have been having with multiple values in tags. Perhaps they should be disallowed because of the ambiguity surrounding their use, not that there aren't already enough headaches with id3v2.x, but . . .
The issue is that mp3tag won't allow corrections to stick with wma artist tags that have multiple values (\\ separator) and sometimes incorrectly duplicates them: when duplicated, then they can be cleared only when all the values are cleared, but the duplicates reappear next time the multiple values are added again. Here is the earlier post:
Splitting multiple entries in a Tag value
(btw, thanks for the great program. it's hard to find a program that deals consistently with multiple values in tags. e.g. itunes doesn't support m4a multiple values in tags. wmp has better support for this, on wma & mp3 files, but doesn't play aac files yet etc. Possibly, despite their convenience, their use should be discouraged b/c of the generally problematic support in software for them.)