Minion with zero hp still alive?

So, I was playing a custom game with Yasuo when this happened (1 v 5 practice game vs the bots). During the game a caster minion got to zero hp, but it didn't disappear like the other minions when they die (like you could still see it was there. It just wasn't moving or attacking and had no health). It was near a downed inhibitor when this happened (not sure if that matters). Anyways I know this isn't a game breaking bug or anything but thought I'd mention it. Will be happy to answer any questions about this.