Since 1.12, items inside a crafting table, an enchanting table and others don't drop to the ground anymore when the interface is closed but go back into the player's inventory. This doesn't happen when leaving the trading GUI.
For example, if I put paper in the very left slot and close the interface, the paper will drop on the ground. I expected to see the item go back into my inventory. Hence, this is inconsistent with the other GUIs.
Could we get the word "villager" added to the title? That might have helped me find this bug report when I was trying to avoid making a dupe. Although I feel dumb for not searching for the word "trading." (Sorry about that, BTW.)