[Gameplay Bug] Thresh's Ult Stops Illoai's E

I was in a game last night with an Illaoi on my team and an enemy Thresh. Our Illoai tried a few times to E the enemy Thresh after he ulted. Each time the tentacle would stop when it hit the wall of Thresh's ult. I'm unable to test it in a custom as I don't really have friends to do so....