Duplication through end/nether portals multiplayer

It is posible to duplicate items in minecraft 1.6.4 and higher.

The way to do this is to make a railway, that makes the minecart drive into nether or end. The minecart must be a minecart with chest, and you wanna put in the things that you wanna duplicate, into the chest on the minecart. Thereafter you push the minecart, quickly take out the things from the chest on it, and go into the end or nether, where the minecart will be - and the things will still be in that chest too, so they're duplicated.

I saw it here: http://www.youtube.com/watch?v=RKmC-LcmVAI
And thereafter I tested it, and found it working.