The bug is that chest carts dissapear when going into the nether, the cart was on a track and ran onto another on the other side of the portal.

To recreate the bug you need to
1) build a nether portal
2) build a track into it on both sides of the portal(in the nether and in the real world)
3) get a storage cart and fill it with a selection of items then run the minecart through the portal

and when i did that it had dissipeared when i came through myself to get the items