Fives zeta TM bug?

ZZPadme lead, JKA, Rex, Echo, Fives with zeta on Domino Squad vs. a full Geo squad. I modded Fives with high defense and almost no speed, and lo and behold the geos swarmed Rex over and over again, while Fives stood there like a bump on a log not gaining any TM so he could taunt. Is this WAI? If I read the description correctly, he should be gaining 15% TM per hit on a 501st ally. That's 90% since Geos hit 6 times per turn.