AlbumSortOrder Tag

I'm quite the newbie, so forgive me if this is a ridiculous question :slight_smile:

I'm using the iTunes Sort fields to organise my albums by artist and the order they were released (eg for Led Zeppelin in the "Sort Album" column I've got Led Zeppelin (1), Led Zeppelin (2) etc etc) and I was filling it into the AlbumSortOrder tag in mp3tag.

I've noticed though that if I subsequently use itunes to edit a file, for example to add a comment, the AlbumSortOrder value is wiped the next time I load the file in mp3tag. I haven't noticed this problem in any other field, is there a way of fixing it or am I doing something wrong?