Vlad pool interaction bug? [GAME]

So i was playing around in an aram, and rolled vlad. gear up expecting a good fight, and then i find zilean killing me nonstop. normally, thats just embarrassing. but here is the thing. I enter pool form, and his bombs still do a hell of a lot of damage, when i feel i should be immune. is this a bug, or is this intended. Team tld me i should report just in case