I've got a few from my most recent project.
I don't even know how I pulled this off.
This is when AFEVs screw you over.
Actually, this happens when you use event ID 0x9C.
To clarify, I am at first trying to trade items from Forde's inventory to Joshua, I move to Joshua's inventory, I try to trade swords and move back to Forde's inventory, and I finally give in and trade the vulnerary.