It only happened once, but I used my ultimate on Fizz at the exact moment he used his E, and my ultimate went on full cooldown, and the ult was completely nullified - no stat steal, death realm, etc.
EDIT: Guess it is intended. Seems counter-intuitive, but alright.
Not a bug. You can cancel it easier than that. A vayne timing an r/q perfectly can cancel mord ult.
I think it reads in the ability description that Morde slows the target for 0.5 secs before suppressing it into the Death Realm.
So if you go untargetable during that 0.5 secs window, the ability gets cancelled and put on full CD.
Yeah like everyone said, the ult has a cast time from when he raises his hand to when it actually goes off. If you play a champ like sivir morg or nocturne you can literally just see him raise his hand and selftarget your spellshield xd.
Anything that renders the character untargetable or stealthed will put Morde's ult on full cd, which I think was a smart decision because his ult is game-changing, and to be able to remove it from a teamfight by a well-timed ability adds counterplay to it
