Hi there!
I have searched for a reason, but didn't find any... Hope someone can help me.
I tried to use MediaMonkey to tag some MP3 files (only added composer). After tagging I checked the tags with MP3tag. But there is no composer field, neither in "Extended Tags..." nor at the left pane (composer field is empty). I checked the file properties with Windows Explorer and there the composer is visible! Now I am a bit confused. Why does Windows Explorer (and MediaMonkey) show me this field, but MP3tag can not show any information?
Do your files have APE tags before you change them with MM?
MM changes only the ID3v2 tag and Mp3tag won't see these changes unless you disable reading of APE.