Bug

I had some problems during the last game i played, I picked chogath on mid and my opponent was fizz. Every time when i tried to harass him with my q he could walk throught my skill and killed me. First i thought he might used some skill of him or went in to my q when it's animation nearly ended. But NO!!!!!!! He realized the bug and took the advantage. He was dancing in my q for real. After that i hope someone can tell me about that more. Thanks for help in advance.