Inventory items disappear when moving them

When trying to move items to the active slots of the inventory using SHIFT and clicking on the item in the inventory, BUT all the active inventory slots already have items in them, The item you are trying to move disappears.

What I expected to happen was...:
I expected the item to not move or do anything, since i was trying to move it to an occupied space.

What actually happened was...:
Items disappeared!!!
Steps to Reproduce:
1. Open inventory
2. Fill the bottom row (active slots) with misc. items
3. Put an item in an above row in the inventory
4. Hold SHIFT
5. Click on the item in the above row.