Warlord's Bloodlust Keystone Mastery doesn't seem to be working for some reason

I was testing out a new build for Attack Damage Carry Twisted Fate and once I bought a Rapid Firecannon, my crits were not triggering the Warlord's Bloodlust keystone mastery. I checked for a reason why it wouldn't trigger but I couldn't find one. I was doing about 250 damage per crit, so I should I have healed about 38 health and received Attack Speed, but that didn't happen. The icon for the effect didn't show up on the hot bar either. I even tried another champion, Ezreal, but it didn't trigger with Critical Strikes. What was really confusing was that I could see the mastery working for other summoned in the very same games where mine wasn't working. I'm not even sure how to reproduce the bug, except to build crit and AD, and see it not work for me. Other people told me they aren't having problems. This bug has occurred for every game I use the Keystone Mastery in.