Ghost Items from Trading with SHIFT-click

If a player try to buy items from the villagers with SHIFT-click, he/she will get the correct number of the items. After the trading window closed, some emeralds pop-out and some of the items become "ghost" items. It will be replaced by other items from trading, or just disappear after the player re-enter the game. I've tested this in Minecraft 1.4 without any mods.