I loaded up a new world and was playing the game like normal until I died in a cave by a skeleton. I decided to log off after that by shutting down my computer while I was still in game. When I logged on the next day, all of my items were on the ground and in my inventory leaving me with 2 diamond pickaxes.

Steps to Reproduce:
1. Have whatever item is in your inventory that you would like to duplicate.
2. Die somewhere.
3. Shut down your computer then log on and get your items back duplicating said items.