Fizz getting hit my Trundle's pillar while "invulnerable" during his playful/tickster

It's been happening on Ascension. I'll go up on to the pole for Playful, Trundle will throw up his pillar while I'm still supposed to be invulnerable, and the pillar still pushes me and doesn't let me use Trickster. So he's basically interrupting my skill while I'm supposed to be invulnerable. The first time it happened, I thought maybe I just didn't see it correctly, maybe just was spamming E too much and trickster'd wrong, but it happened several times again after that, and I'm 100% positive I wasn't trickstering the other times.