I feel like this Twitch bug has been around for a while now...

https://youtu.be/RU8JhiY-Mt4?t=26s

http://boards.na.leagueoflegends.com/en/c/bug-report/ttEfjfxn-gameplay-twitch-e-animation-going-through-but-it-doesnt-do-damage

As a Twitch main, I have seen this and reproduced this MANY times...

Really annoying. Especially when it kill-blocks me.