Pantheon and Essence Reaver

I was messing around on a custom game, and I think I found a bug... Pantheon, when he has one point in E, will crit when the minion is under a certain amount of health, and essence reaver is supposed to give 3% of your maximum mana back per crit. So when I would last hit a minion via a crit, I would not get the mana from ER.