There is a new ( ? ) duplication glitch that involves rewinding time a little, and requires your computer to overload and Minecraft to crash. However, unlike others I believe there are multiple ways to exploit this one glitch. I have found at least two ways to dupe items wit this.

1. If you die, then your game crashes when still on the 'You Died!' screen,  when you log back in, the game will put you back a few seconds before you died with all your items on you, but, the items you dropped on death the first time will still appear on the ground, so, theoretically you can obtain infinite items of anything.
2. This version of the bug was one that actually happened to me (NGL I saw/tested the other one from YouTube). I had placed a shulker box on the ground maybe a minute before my game crashed, put a few of my items in there and then left it there, to go do something else. When I crashed, then logged back in, I was back at the shulker, which was full of the items I put in there. However all the items were also in my inventory, as well as the shulker! 

The second variant of the bug I think would be harder to replicate, but the first example is very easy to exploit especially if you just use fall damage to kill yourself, so when you spawn back in its very easy to collect your items, so I think its important that its fixed!

Thanks!