So my idea involves blocking certain parts of your connection while doing a trade or mail, so that either your comp doesnt see anything happen but the server does (block incoming) or that the server wont see anything while you do (block outgoing), then quickly opening the port back up. I think the game will get the new data from you saying you still have the item and therefore keep it.
I wanna try it out, but need someone to trade with. PM if interested
EDIT** Im in NA