When additional comment frames are added to mp3 files it results in multiple comment frames with the same language. I think in this case the comments should have different content descriptors?
"There may be more than one comment frame in each tag, but only one with the same language and content descriptor."
http://www.id3.org/id3v2.3.0#head-31c41e86...f84f7d2c8d39684
Likewise one could inadvertantly create illegal tags with multiple USLT frames with the same language. Is this a case of user beware or should we get a warning?