Sion ult channel continuing after collision

I smartcast ulted as Sion, instantly running into an Arcade Riven knocking her up. I believe the animation played but I can't be certain since my attention was directed elsewhere. After this I could not auto attack or use other abilities, but could still move normally, and the direction indicator and channel bar for the ult were still displaying on my screen. This effect ended when the channel bar ran out.

Link to the match history for that match if that helps.