Teemo Stealth aa cancel bug?

I was playing a bot game today (2/17/2016) and I was idle between CSing. I gave an auto attack command and the animation started. At that moment, my stealth passive kicked in, Teemo stealthed, the auto canceled itself, and I missed the cs. I would assume this is not the intended way his stealth is supposed to work. I had around 30 ping at the time.