Yeah, but what I don't understand is, you've obviously written the ID3v1 tags yourself (or made sure they were to your liking), but where did the ID3v2 tags come from? Were they there originally, or has some other software mysteriously taken the law in to its own hands and written them in against your will?
Naturally, this has got nothing to do with Winamp, because it only displays what's already there. You can only change the actual ID3 tag structure for an individual mp3 if you edit the File Info box (Alt+3) & click "Update".
In future, it'd be wise to edit the ID3 tags for each new mp3 as you acquire them!