Is this a bug with Akali`s Shroud?

I had a game yesterday playing Akali jungle and was at low health trying to help kill this Zed.

He ulted me so I was like just thinking to myself how I was so dead at that moment. I used my shroud and it cancel his ult...

I was a bit surprised and we ended up killing him.

Is that suppose to happen or is this some kind of bug that I just found out?