Derailed minecarts can be phased through blocks using pistons and gravity blocks

Steps to reproduce:

1. Build the following setup:

   [media]

2. Break the rail

3. Place a gravity block next to the stone bricks/under the piston

4. Activate the piston

Observed result:
The gravity block pushes the minecart into the block below it, making it phase through that layer if it is only 1 block thick.

Expected result:
The gravity block lands in the minecart without pushing it below.