I think I have found a problem with MP3Tag. I've been using it for quite a while and I love it, but quite often I thought the tags in the files were bad.
Now I think it might be this instead.
I just downloaded some files with both ID3v1 and ID3v2.x tags in them. It would appear that MP3Tag ignores the ID3V2.x tags if there are ID3v1 tags - even if I tell it NOT to read the ID3v1 tags by unchecking the box for ID3v1 tags in the options!
Can anyone confirm that this is happening?