[Gameplay] Ashe Arrow Phasing?

I was just in a game of Hexakill on Twisted Treeline (normal matchmaking) where several times the opposing teams Ashe fired her ult with marksman like precision only to have it PHASE through the target. The Ziggs on our team should have been hit at least twice that I saw. Multiple people saw this and all questioned why that had happened. It was a dead on shot. I would assume this is some sort of bug as it happened more than once in the same match. Anyone else having similar mishaps?