I've noticed a very strange bug. When using the foobar2000 player and alterting tags with it, MP3Tag will no longer read tags from the altered file(s). Now, I don't think it's an issue with Foobar itself as, after altering the tags with Foobar, I've checked the files in both Tag&Rename and The Godfather. Both of these tag editing programs read the tags fine.
I know fixing this will probably require huge changes to the ID3 (I didn't try it with APE tags) reading library thingo you use now, but I really prefer MP3Tag to all the alternatives.