Doubled up TNT Carts creates huge lag ("Nuclear minecarts")

If you get TNT carts, and just hold down when you place them on a rail, they will be doubled up in the same place. If you then push them, and they are about to fall off the edge, they will get stuck together, yet still continue gaining speed (You can tell from the sound). Furthermore, you can then destroy all the blocks under the connected rails, and the rails will float in mid-air. Eventually, the game will lag-out and crash, because of "ticking entities"