Minecart carries on going if it falls off the track. 0.8.0 alpha

When a minecart is going on a loop and it goes round a sharp bend it gets stuck and will not move, it also won't let me go near it. If I destroy the block under the track then the minecart goes off in a random direction and doesn't stop until it tries going up a block. it goes the same speed as on powered
Rails. It needs more than one minecart to get stuck like on the first picture.