Music tagging Issues

I have used Mp3Tag to tag all my audio files some of them are in mp3 and some in flac formats. I don’t have any issues with artist, albums, coverart etc. But the ‘PUBLISHER’ and ‘RATING’ tags has some issues. In the sense that the Kodi scrapper recognizes these two tags in the MP3 files but not the FLAC files.

Since its working for one format, and not for other I have to assume this is a bug. Can someone clarify?