Use of TXXX:Work instead of TXXX:WORK is a problem since ID3 tags are case sensitive so you if used Picard and MusicBee or SongKong then you could end up with TXXX:WORK values and TXXX:Work values, it wouldn't really be an issue for Flac (though use use WORK anyway) since tags are case insensitive so the later app should overwrite the earlier tag. Also any applications that do not consider TXXX fields in a case-sensitive way could have undefined behaviour if a file contains both a TXXX:Work and a TXXX:WORK field.