Tibbers Interaction with Crystallize

I don't have video of this, but when I was playing as , (Blackfrost Anivia specifically) I tried to wall Tibbers away from me, and I'm not sure if the wall was in front of him or if it landed on top of him (I think the second one was more likely) he walked right through it, rather than getting knocked back like champions or minions would when the wall lands on top of him. I didn't have any other problems like this one for the rest of the game (though I didn't try to recreate the situation) but I'm pretty sure that one time he walked through the wall rather than getting knocked back.