I'm not sure if this is actually applicable to FF4A (probably not, but meh).
Anyways, when you do the Golbez-Tellah battle, Tellah should be doing magic damage in multiples of 5, assuming he is unequipped and hasn't had his Wisdom changed (16 Wisdom/4 + 1 = 5x multiplier). For some reason, he doesn't do magic damage in such a manner for that only battle.
Go figure.