The custom nitwit villager trade menu close it by its self. When you put a "buy-item" in your hand. Then the villager shows the "sell-items" in his hand. 

What I expected to happen was...:
The menu keep open until I closed.

What actually happened was...:
The menu open for very short time and closed than.

Steps to Reproduce:
1. Summen a nitwit villager with a costum trade.
2. Try to trade with the villager.

I tried to do this with a long command which worked in 1.14.2 and in 1.14.3-pre release 3. When it help can I send it laiter.