Villager (Librarian) doesn't lock trades after first trade

I have been building a Librarian hall

When a librarian has gotten an enchanted book I want, I'll do a single trade (usually paper), to lock that trade in, then move the villager into the cell for that enchanted book.

I have had at least 3 individual villagers lose their 'locked' trade after saving and reloading.

To reproduce:

 1- have a small swarm of villagers

2 - put down a lectern

3 - trade paper to the villager

4 - move the villager to a new location.

5 - break the lectern

6 - install lectern at new location

7 - shutdown and reload.

 

I appreciate all of your hard work.