Gameplay bug : Some champions are able to use cc while ulted by Warwick

Hi there. By buffering your cc when warwick jumps on you, you still cast it even if he applys the spell on you. I noticed it before even seing the video. Once I was in a game and I ulted a Cassiopeia. She was hit by it and the cc correctly applied, but she casted her ult and canceled me (I am sure she wasnt even casting it when I ulted).