Cho'Gath's Q?

I top laned Garen vs Cho'Gath and Cho'Gath's q was stunning me after the knock up instead of just slowing me down. Cho'Gath was blue team I was purple team. This was causing severe CC to the point where half my health would be gone after each initiation. The knock up, stun, and silence combo was deadly. However, a few days later I played on the blue team with a Cho'Gath who top laned against the opposing Kayle. The knock up didn't stun I don't believe, but I wasn't paying much attention. May be a bug since it only happened to stun me, Garen, and not the other champ Kayle. I have not tested this either, this is just from a two game experience.