[GAMEPLAY] Cho'Gath Ult

A bug with Gho'Gaths ult. How it is suppose to cut the cooldown and mana cost in half if you feast on a minion or monster. I have played him a few times the past few days and it only cuts it in half sometimes when I feast on a minion. MOST of the time when I use it on a minion it is completely full cooldown.