So I've been testing all kinds of stuff, and it just wouldn't get it right. I've been going through a simple level by hand and it seemd to go to the wrong leaf at the end. Then yesterday I finally found out I had to get leaf number -(leaf+1) instead of -leaf.
Then this morning I checked the docs to see if that was in there as well, and it was :(. That'll teach me to read quickly! But at least now it's working :D Next stop is fixing the quaternion interpolation in the Doom3 models.