Zombie Villager turning into old Villager

During normal gameplay, I found a zombie villaer and tried to turn it (didn't pay attention to its clothes). After it turned back to a Villager, I found out it was a farmer villager from earlier versions, and it had no trades.

After this, I tried opening a new world on creative, spawning zombie vilagers via spawn egg, and then curing the zombie villagers that had the old version clothes, which resulted on the same farmer villager. Screenshots attached to this report.