WW/Fiora Ult Interaction: uuuuh is it supposed to do that?

Just played an ARAM as WW against a Fiora. I consistently was able to effectively cancel her ult with my own. It was happening either by me ulting her at the same time she ult someone else, or possibly by me ulting her AFTER she ulted someone else, while she was traveling to her 1st target. The latter is what seemed to be the case because after the 1st time, I was able to do it perfectly the next 2 times she tried to ult.

In the end my ult would go through as normal, with fiora helpless in my clutches. Her ult would do no damage and go on cd as normal.

Is this supposed to work this way?