Minion dies for no reason! (bug)

I was playing mid lane against Gangplank as Jayce (very meta, I know), and I was cs'ing, minding my own business, when all of the sudden, a minion decides to die just before I can auto it! I watched it over and over in slow motion, and there were in fact two minions hitting it, however, it died in between the minions attacks. So, either one of the minions attacks were delayed, or the minion just died from the shock of knowing it was about to die, who knows. You can see what I'm talking about in the link at 24 seconds video time (1:54 game time).

This seems like such a small thing, but at the time, it was quite tilting to see my 3rd cs die for no reason :(