Duplication glitch for every item (eg: shulker boxes)

The bug

This duplication bug has been around for quite some time, but never reported here. (found no tickets reporting this)

You can easily dupe every item in singeplayer and multiplayer, and this also can be done in survival.

I strongly advise to watch my video so the last steps on how to reproduce are more clear for you. Link to the video: https://streamable.com/6w2o4

How to reproduce

1. Create a world with cheats on (just to make it easier), and find the end portal.
2. Build the setup as seen in the screenshots.
3. Turn on the end portal, and remove the first two rows of end portal blocks, you can do this by using lava in survival mode, right click the with a lava on the end portal frame blocks.
4. Now, spawn and tame a donkey, llama or mule. (ill be using a llama)
5. Equip it with saddle/carpet and a chest. 
6. Fill the entity with what you wanna dupe! Example: I'll filling it with shulker boxes full of totems and diamond blocks 
7. Now, you gotta bring the health of your entity to half a heart, you can easily do this by throwing potion of poison II at it.
8. Push it into the water on the side, and than push it 'hard' into the lava.
9. Observe how it drops the items, you expect it to be dead but if you go into the end.. SUPRISE! it will be well and alive with your items still in it.