I have recently realised that Apple stupidly changed the way they treat the "Grouping" information for tracks within iTunes (I'm on 18.104.22.168 Windows 7 x64) - reading/writing this information now to a new tag called I believe "Grp1" whereas before it was something like "ContentGroup". So, I updated MP3Tag to v2.81 so I could see this tag.
I'm working with an .mp3 file. When I edit the "Grouping" tag in MP3Tag Editor, all the changes are correctly reflected in iTunes ("Grouping" field) except when I erase the tag contents (or set it to ) - then iTunes still shows the last non-empty tag content, not the empty content. If I close and re-open MP3Tag Editor with this .mp3 file, it still shows as a blank tag, but iTunes refuses to show this. Any changes I make the other way (ie edit in iTunes) work fine, including a blank tag.
I have tried this with MP3Tag set to read/write ID3v1 & ID3v2 tags, and also just with ID3v2 tags, with the same result.
Is this iTunes messing up or something in MP3Tag? I realise this "Grouping" tag was added in this latest version...