I don't know if this is just the game working properly, but while playing today I was running away from Galio, pooled, and then was taunted while pooled.

Basically I pool, Galio ult's while I'm still in liquid form, and I proceed to run towards Galio while pooled and attack him when I come out of pool.

I'm not 100% sure, but this might be intended. Galio's ult is AOE, and not targeted. Vlad's pool only makes him untargetable, not invulnerable. Some other AOEs can hit him in pool, so this might be intended to do so as well.