When placed on an active Powered Rail, the minecart repeatedly does a flinching animation as if the player was punching it. Any attempt to ride the cart will immediatly make you exit the cart upon boarding it. No other rails do this, including Powered Rails not activated by a redstone current.
Normal. In the screen shot you have the mine cart on an activator rail not a powered rail which shakes a normal minecart and ejects any mobs in it out.