After syncing iPad, most of the music (40gb) appears in "other" - how to properly categorise?

I have large "other" category on the iPad which i think is a duplicate of the music stored on it. Problem is the "other" files are taking up over 40GB of space - even more than the music.

After trouble syncing music, I de-selected music slams and reinstalled. This successfully reinstalled the actual music, but I have this residual "other" amount that I can't budge.

I have tried re-syncing; add a bit of music or take a bit of music off. So far nothing seems to allow the sync process to recognise the "other" as surplus and remove the files.