Is Cass's Miasma supposed to block Illaoi's test of spirit?

I can understand that it blocks Illiaoi's dash, but why does it also instantly put test of spirit on CD and block the projectile that grabs the enemy champion's spirit? I feel like that needs a new interaction. I was just in an ARAM and I coudn't seem to cast E through Miasma, and if I cast it in Miasma it went on CD immediately(illaoi went through the motion of casting test of spirit but nothing left her frame in the form of something to grab an enemy champ's spirit.