Blue Side Vi Ult Gets Canceled By Red Side Yasuo on ARAM

Blue and Red just meaning Vi and Yasuo are on different teams. Not sure if this is a bug or an intended mechanic.

I ulted Cass and she ulted back. I know that Vi is vulnerable during her charge.

However, I also ulted a Yasuo, and it seemed by the nature of ulting he was allowed to Ult me back and cancel my ult. I didn't seem to get hit by a tornado. I'm not sure if this is an intended mechanic, but it seems strange to count Vi's ult as a knockup on herself to let the opposing Yasuo in.