The case of the mysterious double ult

This has been happening on several different champs, I noticed the glitch Leona, Lulu, and Nautilus. I would ult, and if it resulted in a kill my ult CD would reset and I could immediately ult again. It doesn't happen every single time, but it happens enough to make a difference in the game. I also experienced similar things with health pots. Id pop a red health pot, and if I killed an enemy while I was health regening my health pot would come back. I asked several people if they had similar problems, and they all said that they were experiencing the same Ult problem but not the health pots.