Cho'Gath Feast Cooldown bug

Sometimes when i play Cho Gath, if try to feast on a minion that an allie is slaying at the same time, the feast will still go on cooldown, even tho i didn't get the credit for killing the minion and I also didn't get my stack. Now i don't have anything to prove that but it actually occured to me 3 or 4 times already. As far as i have spectated, to recreate the bug you just have to hit a minion who is getting killed by an allied champ with your feast, its pretty hard to do as i said already, however its definetly possible. Has this ever happened to anyone else?