I don't know if it is a bug, but here it is:
If you set the "uses:"-tag of a custom villager trade to 1 or higher, it will unlocking new not custom trades, like it does normaly. It should not, because it should only do, if you're trading "new" trades. New trades have (custom or not) a "uses:"-tag of 0. So if you set it to 1, it isn't "new" anymore.
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Comments 3
You've guessed it, what i want to do. But myy Idea is, that you set the uses:-tag to 1 or higher, so the villager thinks, this trade isn't 0, so it have to be "old". Every new trade has a uses:-tag of 0, no matter if it's a custom or a naturally spawned villager. Even if I set the uses:-tag to 1 or higher, it will be unlocking new trades. It should not, because I made an "old" trade.
Er perhaps, I'm wrong again. See MC-48929
I don't believe there is a way to prevent new trades anymore.