If they want duping to stop can't they just make it if you want to drop something you CAN'T. You have to trade it, and as soon as the trade is successful the game auto-saves. Good idea? Or is it flawed?
It's creating an actual problem to deal with a perceived problem. It would make it harder to manage items when your backpack is full, just because a couple of players don't like seeing other people share toys with each other.