Put the summary of the bug you're having here

What I expected to happen was...:
When trading with villagers I expected to sell item (9 coal) for a single emerald.

What actually happened was...:
When I put the coal in the trading menu with the villager and click on the emerald the amount shown on the coal still in the trade menu is the correct amount. However, when I take away the coal it subtracts a random number from the coal giving me less than what should have been given back.

Steps to Reproduce:
1. Trade with villager until his trades are locked out.

2. Wait for villager to replenish trades.

3. Continue trading and the bug appears.

More Info Shown is this happening with a fisherman villager, however it also seems to be an issue with Farmers and Librarians from what I have tested.