Smite Jungle 50% Cooldown Broke, With Teemo poison

Played a game as Teemo Jungle, the smite upgrade that gives 20 bonus gold and reduces smite cooldown by 50%; Would NOT work on large jungle minions if they had teemos ongoing poison damage happening already. Smite would go off to deliver the killing blow to the large jungle minion, but no bonus gold and no 50% cooldown. I tried this on 15+ jungle monsters, all different jungle buffs. Never worked. It DID however work on a jungle monster that did NOT have teemos ongoing poison damage to it.