When I upgrade a working villager to a MASTER class I can't trade from him anymore. The "shop" window opens for a milisecond and closes immediately. I tried to save the world and open it again but no results.
Environment
Windows 10
Geforce GTX 950M
8 GB RAM
Intel Core i7 - 7th Gen
Java build 1.8.0_171-b11
Duplicates MC-154201 (fixed for 1.14.4).