Gangplank Farm Bug

I was playing Gankplank on a normal matchmaking game, and I had around 370 farm, was going for 400. All of a sudden, my CS went down to 330. Whenever I killed a minion, the number jumped up to what it actually was for a split second. The 330 number kept climbing with my farm and went back and forth every minute or so to my real farm. Game ended and my farm was 370-ish (Really had 430-ish).

Don't know if this bug applies to any other champions, but just letting everyone know.