Activator Rails don't always eject mobs

When the cart in the picture is moving clockwise, the cart 'jiggles' when it goes over the activator rail (under the cart in the picture) but the pig does not eject.

The pig does eject when the cart moves in a counter-clockwise direction.

I expected the pig to eject without regard of direction when going over an activator rail.

When reproducing this bug be sure that the activator is on the X-axis (Red in screenshot) as I believe that does make a difference.