Is this the sequel to
TBH: I don't understand your problem.
Could you show us a real example of a file what you expect to see, what you actually see.
Especidally interesting would be the extended tags dialogue of a single file and a screendump of the settings in File>Options>Tags>Mpeg.
And: could there be a misunderstanding? MP3tag is a tagging program but not the tagging standard for mp3s.