Cassiopeia's Ult.

Recently I watched a stream. He is trying to learn Cassiopeia but has some difficulty as the ult seems to be bugged. For example, If Taliyah uses her q, she is left unaffected by the ult. Also it seems to be overall inconsistent. It doesn't define what is facing her and what isn't very well. Thank you for your assistance with this matter.

Concerned Summoner, Charlie Silver.