The sound effect, or the slowed effect? Or do you mean the bonuses on the champ with Kill Sense stay after a nearby enemy champ dies?
The slowed effect stays after the champion with Kill Sense dies. I think it's a known bug that hasn't been fixed yet.
Yes, this is a known problem with the ability. Right now the new game client is our primary focus, but this one specifically is on our patching list for the future.
