If you have no empty slots in your inventory, there are items in the trade slot (but not enough to complete a trade), and you have more of that item in your inventory, you cannot click on the trade to complete it.

Steps To Reproduce:

1. Summon/Spawn a villager
2. Fill your inventory with a random (non-tradable) item, leaving 2 slots open
3. Fill the last two slots with a stack and a half of a tradeable item
4. Trade with the villager using the stack of 32 (leave the remainder in the trading slot)
5. Click on the trade button in the menu again to attempt to autofill the trade slot with more items

Observed Results:

Despite you having another full stack of items which can be used to trade with the villager, they will not be moved to the trading slot in the villager's GUI.

Expected Results:

The full stack within your inventory would automatically fill the left over remainder items to the max stack, allowing you to complete another trade.

Screenshots/Videos:

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