When you are in your inventory screen on creative mode, and push Q to drop an item, you pick up two instead of one(only tested with stackables)
Steps to reproduce:
1. Open in creative world.
2. Open your inventory.
3. Grab any stackable item(in my case redstone torch)
4. Go to the player inventory tab(or else Q will not yield any items).
5. Hover over any stackable item(in my case it was on my hotbar at index 8)
6. Push Q
7. Congratulations, you should now have one more of the item then you originally had.