IF I have a container(one that is on the ground) open on my screen, and then proceed to do and complete a trade with another player, despite if the player has his/her backpack/container on them opened, I will open there pack on my screen upon both of us clicking accept on the trade. It is random, have yet to discover the bug, but sometimes i can get it to stay open othertimes it opens it and instant closes it. I tested being as close to the person as possible and it will still open and close it, distance isnt a variable with it. its all random on whether it stays open or not, but it does at least open the other players bag every time. WHEN it does stay open,,, I can totally pick one item/stack of my choice and move it to my bag despite how far away the player is.

1.Open Container on ground and my backpack
2.open trade window
3. Accept trade
4.Container on ground will close itself and the other players backpack will appear on the screen
5.Drag and drop 1 item from their pack to mine.