Villagers that have been zombified and cured have a slim chance to change the item they were trading to something else.

Prior to zombification, this villager was selling knockback II. After curing, he now sells a bookshelf. The bookshelf is discounted, and he has the experience from when I locked knockback II, but he is no longer selling knockback II. I am so thankful that this bug happened to nobody else, especially not my mending.

Steps:
Give a villager a job. Note its offers.
Lock the offers by trading with the villager.
Zombify and cure the villager.

Expected result:
Villager should sell the same things it sold prior.

Actual result:
Villager may sell something else entirely.