Tahm'Kench Devour bug (Gameplay)

When I play as Tahm'Kench, my W (Devour) acts... strange. Half the time, anyway.

1. I cast devour on an enemy minion.
2. I eat the enemy minion.
3. I can't spit the minion out, it tells me that it's on a 12 second cooldown.
4. I spit the minion out after a few seconds, but not by my own will.
5. I try to eat another minion, it acts normal.
6. I eat another minion, the bug happens again.