SongKong appeared to add YEAR field to Flac file but wasn't readable by metaflac indicating some problem with how it was written, don't see that it can be specific to this field more likwly the order of events causing the issue
jaudiotagger is assuming a VENDOR string is saved and then undercounting number of vorbiscomments, this means the last field written is not actually readable when there is no VENDOR string.
Done.