There's a bug with Kalista and Karthus where she can fling him/ re-position him when he's dead, there's a graphical bug with Teemo's poison that appears on occasion and stays permanently on a champion until death, there's a bug where Ezreal can arcane shift out of Thresh's and Blitzcrank's hook if timed right(may be intentional), Shaco can use bond of stone with his clone so that the clone takes the damage(may be intentional).
I have a few matchups that I think can yield a bug effect but I haven't tested them yet. I'll update when I've tested them properly.