TU47/CU37/1.40/Patch 16, TU48/CU38/1.41/Patch 17, TU50/CU40/1.43/Patch 19
Xbox 360, Xbox One, PlayStation 3, PlayStation 4, PlayStation Vita, Wii U
When trading with A Villager.
Selling 1x Emerald
Buying 16x Wheat
Now if you have 1x Wheat in Slot 0 for example this works in all slots
and you have 16x or 17x Wheat in another slot when you press A to buy that trade it will use the 1x wheat instead of spending 16x wheat this is Game Breaking and has been tested in Survival and in Creative.
Here's a Link to a YouTube Vid describing the bug in more detail explanation.