I had a game last night where I was starting my ult on a Malz when he started his ult on me and it Suppressed me out of it and normally that wouldn't be a big deal even if your supposed to be invulnerable once it starts but since it "Started" it even took my cooldown so if its intended to be possible to be stopped I should at least get my cooldown back.
Also I'm not sure if this works with Warwicks ult too or even any stun just that it happened with Malz.
I've had it happen many times with a warwick timing his ult on me perfectly with my own. Right at the start their is a super small window of opportunity as well as any time she appears with the blinks where she can be knocked out of it. The blinks are short enough to where targeted skills won't ever have the chance to work but aoe skills can if you are super unlucky.
Working as intended.
Nearly every skill in this game has some form of cast time where the ability can be interrupted.
So yeah. Working as intended.
I love activating 
's E right before I anticipate an enemy Fiora to hit her ult.
Pops her right out of the middle of her blade dance, and 1 second of hard CC usually means instant death to a champ like Fiora.
The less knowledgeable Fiora players then cry about their ult not working in /allchat, always makes me chuckle.
