I used Condemn on Warwick as he ulted me, he was knocked back into a wall and got stunned but I was still suppressed for the full duration and he still finished the entire animation.
Suppressions are weird, mainly because few champions have suppression and maybe riot doesn't really find any glitches with them.
I play a lot of warwick and I see strange stuff all the time with his ultimate. Especially if you time it at the same time an opponent is using an ability. I think I have done what you are describing as well.
Stuff like that is always happening, like when someone dashes when I ult them they are not close to me yet still suppressed and taking damage, it's funniest when you ult akali right as she goes in her shroud cause then you get a weird animation where Warwick is spinning.
