...I don't think Death29 was aware joint texture modes exist

Please make sure your item.dat isn't set to readonly just in case you've been previously messing with your customs and locking them.
Correct TEXJOINT line in your item.dat should look like this:

TEXJOINT 0; 4 4 4 8 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

Also attaching a screenshot of how your tori looks to me just in case.