Twitch Bug?

There is a bug i believe with twitch to where when his ult is active he doesn't do any damage to the enemy nexus. A friend and i just played a game where I tried to backdoor as twitch and turned on my ult to get the extra range, but then i did no damage to the nexus at all! I don't have a video to put as support but you can go try it out for yourself. It happened to me when i was playing on the blue side. I'm not sure if the same happens with both sides.

                 Thanks for your time,
                                      JP