Futaba Sbus Pass Through

I am having trouble getting RC13 and RC14 Pass Through to work on the the Pixhawk.

I am using a Futaba14mz transmitter and Sbus receiver.

BRD_PWM_COUNT=6, RC13_Function=1, RC14_Function=1

RC9 to RC12 work fine

Have i missed something.

Thanks

David Ardis