Multiple contentgroup (TIT1) tags in MP3

[zfc]

Sorry to bother again.

I use contentgroup tags to represent the type of titles (piano sonata, piano concert, ...). And quite often I assign multiple such tags (e.g. concert; piano concert; piano). That works great for flac-files. But I just noticed that my mp3 files only show under the first contentgroup (=TIT1) tag and all others are disregarded. Could you add support for multiple contentgroup (=TIT1) tags in mp3-files?