Minecart go on even if there aren't any rails.
Step to reproduce:
-create a railroad that has got a end
-summon a lot of minecart in a point on rails
-push the minecarts on the rails
-when the rail finishes the minecarts go on the terrain
Sorry for my english but I'm not english
This happens when more than 2 (I guess) minecarts are at the same spot, they will follow rails until they get on the ground and will move infinitly in one direction see MC-14