i had the same problem too, but what i thought was weird and possibly a defect with my game was when i didnt mug a monster (ie.blue dragon) during a fight, itd drop different items than if i mugged it during a fight.

so with saying that, whenever i didnt mug him i tended to get dragon fangs(although still rare)

i didnt have rare item ability either.. i didnt even get to fighting bahamut yet..

dont quote me too much on this, its probably just a defect or weird phenomena with my game :rolleyes2