Item duplication with Minecart with Chest and Nether Portal

If you have a Minecart with chest and a netherportal you can duplicate everything you want

How does it work?
1.Put something in the chestcart
2. puch is to the portal
3.Look in the chestcart en take the item right before the minecart goes throught the portal
4.Now you have to go to the nether and look in the minecart in the nether and if there items in it it is duplicated

More info:
https://www.youtube.com/watch?v=Ku_1G3P0VWA