Bukkit

What steps will reproduce the problem?
1. Player will drive onto a teleportation block underneath a drivable block
2. Player is teleported
3. Player spawns another cart or is either instantly thrown up in the air with the clash of another cart

What is the expected output? What do you see instead?
Player Teleports as normal with no carts spawning, instead, Player spawns another 1-7 carts and/or is either instantly thrown up in the air with the clash of another cart(s). Finally the Cart may end up floating one block in the air instead of dropping. Drops after 15-20 seconds

What version of the product are you using?
v18 - SNAPSHOT-R1 B: #29

Do you have an error log of what happened?
N?A

Please provide any additional information below.
This teleportation block is next to train tracks and is teleported across the train track in hope the player does not go onto the track.

I will look into this later, but on our server; teleport blocks have previously worked fine.