When someone uses a minecart, boat and horses, the person inside travels with them inside. As soon as they go so far, their body appears where they got in. The person aren't really at the place it shows them, they are really travelling but it shows them to be where they got on with an invincible body.

Steps to Reproduce:
1. Get a rail that goes very far.
2. Get them to travel in the cart for a reasonably big amount of blocks.
3. DO NOT tell them to get out.
4. Watch their body appear where they got in their cart, but they aren't really there.

THE SCREENSHOTS BELOW ARE IN CHRONOLOGICAL ORDER OF WHAT HAPPENS.