This occurs independent of the Minecart Experiments being enabled.

Steps to reproduce:

1. Build a nether portal with rails in front so minecarts could be sent through (enough rails so you can step between the first rail and the nether portal).
2. Place a really large amount of minecarts on one rail (with a command block, for example).
3. Step between the minecart cluster and the nether portal.
4. Push the minecart cluster away from the portal.
5. The player gets teleported through the portal.