Shift-clicking an item in your inventory when another inventory is open and full (for example, an enchanting table with something in it, or a full chest) makes the item you're clicking on disappear.

What I expected to happen was...:
I used to click on everything in my inventory to "dump" it quickly into a chest, and things that wouldn't fit in just wouldn't move.

What actually happened was...:
First I accidentally shift-clicked an iron ingot into a crafting table, when a pick was already there, and iron ingot just disappeared. Then I tried to reproduce this bug in a full chest (opened it, found an item that doesn't have a duplicate in a chest, and shift-clicked it), and it disappeared too.

The same happened when I opened a crafting table (you can't just shift-click there, when you do, an item from inventory moves into your hotbar and vice versa).
I filled my hotbar with other items (non-dirt), shift-clicked a piece of dirt, and it disappeared.

Steps to Reproduce:
1. Open an enchanting table / chest / inventory
2. Fill it (hotbar - in case of inventory) with something
3. Shift-click something else you have in your inventory