I have a fletcher and fisherman villager that have locked themselves out completely today. I have a spider grinder I was using to feed them string and would switch with their coal or bow trades to unlock the string if it didn't auto reset. Am I doing something wrong to make them completely lock up? I've never heard of villagers doing this, I thought the last trade would guarantee a reset. To clarify all four of their trades have completely locked out so the villagers cannot trade at all.

You have to trade them 3 different trades sometimes to unlock them, sometimes 2 works though

Right, but all four trades they have are completely locked out now. None of the four would trigger a reset.

Have you tried relogging or something? Because that works for me (sometimes :P )

I just did, still locked out. Unless there's a new bug in 1.9.4 that just decided to appear, it might have something to do with the crash that happened last week while I was gone.

Oh :P

I played a game with some guys who were really into their villagers. They had hundreds. Sometimes a villager would lock out and that would be that. He would have to be killed and replaced.

Another way you could reset the villagers is if you breed them.

Villagers have had the potential to lock out 100% for quite some time now.

It works like this-

Each time you trade with a villager, each single trade, it creates a small % to unlock it's trades. Let's say 5% for the sake of the explanation.
Every trade is cumunulitive when you make the trades, before you exit the trade options.

So, trading for 1 item is 5%, then you put a stack in and get 3 more items- now you have a 20% chance of unlocking the previously locked trades. But trades only can be used 2-12 times before they lock. So, in an unlucky circumstance, you can max trade with only 30% chance of recovery and still fail to unlock it.

Because of this % system, trading single at a time, or very few, locking out villagers is easy to do accidently.
It used to be that the last trade on any locked villager would unlock everything, but they decided to throw that out the window.

Its a pain but it happens.
It's a 20% chance to refresh locked trades and enter breeding mode for each trade. Doing multiple trades at once without closing the trading GUI will not give you a better chance for the trade to refresh that doing single trades at a time. It's just bad luck.

Breeding them is not really a solution, because with mob griefing off you have to trade with them to get them to breed.

All hope is not lost though. You could always use a zombie to infect him and cure him again. Note that this will essentially make a new villager with the same colour robe. He will not keep his trades and might have a different career (i.e. Fletcher could come back as a farmer, shepherd or fisherman instead).

If you're annoyed about this, maybe upvote the bug report!
https://bugs.mojang.com/browse/MC-749

Well damn, I have really bad luck if two locked in one day. I'll just have to cure them again