Minecraft Version: 1.15.2
(modded) forge-31.2.22
fl-3.4.1.jar
flux-4.17.1.jar

In the Online Market if I place something to trade (like a stack of wool) and shift click to get the emeralds, I only get one emerald instead of a few and while it looks like it used the wool, when I pick it up it turns back into a stack of 64. In other words I'm effectively duping.

If instead I pick up one emerald, then another, it uses the wool and everything works fine.