[Samhain]

I'm going to make an educated guess here and say that your Oracle was burning pearls to boost his chances of victory in the duels rather than to reduce what little fatigue it would cost it. I haven't heard of this special case for Magic Duel before, and it is not listed in the Wiki page I linked to above. But, I've got to believe that is what was going on.

There is good nugget of advice in this little epiphany, if you are sending a mage in to battle with the intent of spamming Magic Duel, dump some pearls on him if you want to increase his probability of survival.