Villagers do not charge for the last transaction before locking in

(!)This is a serious bug.

1.Assuming you have 45 emeralds, the villagers can trade with you 4 times at a price of 1 emeralds.

2.You have 41 emeralds left in a deal before the villagers lock in (that is, the 4th transaction),it's right.

3.but when you close the UI, your emeralds will change to 42.