When files are transcoded form one format to another with tools such as DbPoweramp they try to convert the metadata to the new format. But in some cases it is done a bit stupidly. So for example MusicBrainz.org defined for the ID3 metadata format (as used by mp3s,aif) that the Musicbrainz Release Id to be stored in a TXXX frame with value 'MusicBrainz Album Id' but for FLAC they defined is stored in a field called 'MUSICBRAINZ_ALBUMID'
Transcoding an aif file to flac creates a flac field called 'MusicBrainz Album Id' instead of converting it 'MUSICBRAINZ_ALBUMID' because dbPoiweramp only understands the standard fields such as artist, album ectera
We cant change these fields because they are in widespread use, but Ive modified the mappings for newly created songkong/Jaikoz fields so that tools such as dbPoweramp will do a better job when transcoding files, more data will be protected.
One side effect of this is that if you rerun SongKong over files previously processed by SongKong it will add metadata that was already added because that metadata is now stored in a different fields, bu this is a oneoff issue.