I have a Sony Walkman NWZ-E460 Series.

The way picard tags multi CD releases (like release a9f43acb-3c16-4b45-9a5d-ea9d9c57b3aa) causes the Walkman to play the titles in wrong order. Instead of playing "title1/cd1","title2/cd1","title1/cd2","title2/cd2" it plays "title1/cd1","title1/cd2","title2/cd1","title2/cd2". Somehow it can not cope with the format which is written by _save in id3.py (I think thats the place):

254 text = '%s/%s' % (metadata['tracknumber'], metadata['totaltracks'])
261 text = '%s/%s' % (metadata['discnumber'], metadata['totaldiscs'])

So my idea to workaround this limitation of the Walkman is to write continuous tracknumbers, starting from 1 up to totalalbumtracks. So for a album with 4CDs, the track #10 on CD#4 would get number 15+15+15+10 == "55" instead of "10/15":

TRCK: "55/60"
TPOS: "1/1"

If such feature/checkbox should be limited to idv3 tags due to broken MP3 players, or if it should be extended also to FLAC files, no idea.