Intentional or Bug? Blitzcrank Grab and Azir Ult

Is it intentional that a Blitz grab can not pull an enemy champion through a friendly Azir's ult?

I've had a couple instances where the Azir on my team ultra to trap the enemy team while I, as Blitz, try to pull and isolate a carry. But even when I connect the hook, the enemy champion would stop I try to pull him/her through the Azir Wall.

I kind of feel like it's a counter-synergy.