Trading doesn't properly remove the emeralds (and other items in general) needed to trade from the stack

Example 1: Trading for an unstackable item (such as a sword from a Weaponsmith) will either fail to remove X amount of emeralds in the trade or refund the emeralds in full when you remove them from the trade slot in the GUI. 

Example 2: if you trade for all the stock on a current trade (ex. 1 emerald for 3 bookshelves four times for 12 bookshelves for 4 emeralds), you'll sometimes be refunded emeralds that should otherwise be gone entirely.

 

Example 3: Shift-clicking to trade for the full stock on a trade for an unstackable item (ex. the Weaponsmith's trade for an Iron Axe, in which the stock is 4), you'll only receive 1 Iron Axe and you will not lose emeralds or any other item you're trading for that matter.

 

This issue occurs when you shift-click to trade for all the stock on a given trade as well as when you shift-click the item to trade from the trade slot to the inventory.  Trading for stackable items will only refund some emeralds when you trade for the full stock before removing the emeralds from the trade slot.

 

How to reproduce:

1. Create a world in Creative mode with cheats enabled; find a village.
2. Load up on emeralds/any other items that villagers typically trade for.
3. Change the gamemode to Survival
4. Trade around with the villagers, varying from shift-clicking, taking full stock, etc. and see how the villager's economy is all screwed up.