I know there are other threads like this, but I'm just kind of adding more information. All of these get duplicated in the multiplayer beta due to 2 players interacting/breaking the object at the same time. The ones that me and a friend have tested are the casks, bee houses and horses. But due to the principles being the same, it's to be expected that things like kegs, bins of NPCs, or even objects placed on something like a tree (Tapper) would act the same. Another small detail about the horse duplication: The model of the duplicate is messed up. And from what I remember, when the player on the original horse gets off of it, the duplicate horse disappears.
I have to go back and try it again, but I think we had an issue with the fiberglass rod duplicating when I dropped one on the beach for my son to pick up. I was headed back to the farm to do something and he was going to take over fishing at the dock without a chest available. I dropped the fiberglass rod and ended up picking it up right away as normally happens, but he also had one pick up in his inventory as well.
