Villagers allow trades to complete when trade is X'ed out

I've only tested this in 19w14a.

To repeat: 

1. Trade with villager until X appears

2. shift click X'ed out item under the trade window \

3. Shift click the trade window (no item appears in the GUI, but it appears in your inventory)

Video of bug: 

https://www.youtube.com/watch?v=JJ0sSkTXBqQ