How to detect/remove duplicate tag entries?

id3test shows some of my tracks have multiple id3v2 entries, but nowhere in mp3tag is this related/evident/fixable, so far as I can tell. I need to be absolutely sure all my tracks have ONLY ONE tag or my car stereo refuses to so much as acknowledge the tracks' existence.

Now I can fix this by loading the offending tracks in Foobar, copying the meta data, erasing the file's tags, then pasting the meta data back in... but this is awfully roundabout.

mp3val (freeware, goole it) removes the illegal tags.
It is not possible, though, to get the information out of the invalid tags.
Use mp3diags (also freeware) to find the files with problematic tags.

Thanks... why would mp3tag, a program whose sole purpose is to manage mp3 tags, not be able to handle "illegal" tags? Anyways I ran mp3val and it came back with xing header errors on various tracks, but the tags were fixed by my actions in Foobar.

MP3 Diags will find mp3's with multiple tags and will also fix them and you can do it on multiple files at the same time.

It will also find a lot of other errors that can show up in mp3 files.