A bug that's been here for a few patches... maybe a lot longer, but I started seeing it recently
Lucian passive not always proccing when it has available targets right nearby. First shot killed the target. Was like "Oh ok, i'll shoot it again since it's dead. Oh wait you have a passive? oh well.." I stopped playing Lucian because this because it'd trip me up and throw me off my game. I'd just lose several CS while recovering mentally from the 'wtf' of it. Tried it again first time this patch in a while. See it several times in the first game.
It even LOOKS like it hits, but does 0 damage (but the particle goes for the first minion, and the shiny particle of 'hitting' is on the next minion).