Gangplank + Cull Bug

I've been using Gangplank and starting cull in bot games because why not, and i noticed that my cs and the charges remaining on the item dont add up to sometimes. Once i do reach 100 cs, Cull, in this case it said it had 9 charges left. I didnt kill any jungle monsters that game, and i was using some barrels for faster wave clear. So far this has happened every time i did Gangplank + Cull, and im not sure whats causing it