I've seen a few posts over on the league subreddit about this and just had it happen directly to me. I was playing Skarner (using the Battlecast skin if that matters) and ult'd the enemy Zac (default skin) and my ult went on CD and Zac just walked away. These champs aren't exactly in every game but assuming it doesn't work on 1 champ it may not work on others and it's frustrating regardless.
I've seen a few posts over on the league subreddit about this and just had it happen directly to me. I was playing Skarner (using the Battlecast skin if that matters) and ult'd the enemy Zac (default skin) and my ult went on CD and Zac just walked away. These champs aren't exactly in every game but assuming it doesn't work on 1 champ it may not work on others and it's frustrating regardless.
skarners ult is also bugged for Guardian angel and 
ult
Sounds like the Zac buff nobody asked for, but everybody needed.
Can confirm. Happened twice to me in the same game. Ulted Special Weapon Zac as normal Skarner, went on cooldown both times, no damage or anything. Incredibly annoying!
