Kennen Ult bug

Just played a game versus a Kennen using the blood moon skin (don't know whether this is part of the problem or not), and I would get stunned for no reason without him using any spells except for the fact that he screamed "HYAAAA!". This happened 4 or 5 times before I realized that he was using his ultimate, but there were no particle effects for the ult, only the sound.