Villagers are cheating me out of emeralds!

often times when i trade with a villager, the villager will take my items, but not give me any emeralds back. these villagers have discounts too, but I end up paying the regular price. I believe these two bugs to be related to one another.  (speculation)  Perhaps the game is trying to charge the full and discounted price at the same time, with the full price winning out.  as for the part where they take my item without giving anything in return, I've not the faintest idea of how to explain that.