Jayce Hammer Stance Auto-Attack Bug

I noticed that Jayce's auto attack in hammer stance after the passive auto attack hits in a very fast motion compared to other auto-attacks and does not register right away. It does make the sound that the auto-attack has been completed but if you move after right away, the target receives no damage.

You can literally auto-attack - move - auto-attack a million times around the target, Jayce will still create a motion and sound that it has hit the target but the target will receive no damage.

Jayce's cannon form W into hammer stance and the passive works just fine, but it is the normal hammer stance auto-attack that is the issue.