Item Duplication Glitch with Villagers

I was trading with some villagers and when I put a stack of emeralds in the leftmost slot and shift clicked the trade option. I expected to get the amount for 7 trades.

What happened was I received the max amount of trades the offer would let and when I closed out the screen(without clicking on anything else) I saw that I dropped the stack of emeralds minus 8 trades and I still had the stacks of traded items.

To reproduce the glitch I did the following:
Step one - find a villager that would trade one emerald for something.
Step two - get a stack of emeralds.
Step three - put the emeralds in the left most slot for trading with the villager
Step four - Shift click the trade(right most slot)
step five - do not click anything else just close the trade screen with the key binding

It is really glitchy after that. Sometimes I will get to keep everything (minus the cost of 8 trades) and at other times I will have only gotten enough items for 8 trades.