Trading Dupe Glitch

I had 63 wheat, and and planned on giving it to a farmer villager that I often trade with, so he disabled the trade that I did while I was doing it. I put all of my wheat in the slot, and shift-clicked on the emeralds that popped up. The villager stopped accepting the trade half-way through, so I was left with 42 wheat, but I had 2 emeralds.