If a minecart on an ascending rail is pushed against a block behind the rail, it will begin to float above the rail. This happens only with Minecart Experiments enabled.

Steps to reproduce:

1. Build the layout as shown in the image/video (a rail track that ends on an ascending rail against two blocks).
2. Place a minecart.
3. Push it up the ascending rail against the block.
4. It floats above the rail.