[8.3] Sion R Cancelled by Bard Q

If Sion presses R after he is hit by Bard Q, but not yet stunned, as it has not yet hit the second target, his ulti starts up, he takes one step, then stops. This happened to me accidentally, and I don't know if it's 100% certainty. I also don't know if that interaction happens with other "Unstoppable" ablities, (Warwick R for instance). The timing is quite tight and I haven't had the opportunity to reproduce it.

Here's a video of it happening : https://www.youtube.com/watch?v=qwV9jFSWstU&feature=youtu.be

As you can see, Sion is "Stunned", "Unstoppable", and "Stunned" again.