Settings of SingleCopter

I am setting up a SingleCopter using Revo as FC flashed with latest Quad firmware with Frame type set to 8.
The servos do not move in response to rudder stick. All other channels (ail, elev, thr) work.
Pls note, in Radio Calibration page of MP. the green bar for YAW moves left/right corresponding to rudder stick movement , meaning there is no problem with the FC and receiver.
Things I have tried :–
— swap another FC, — reboot and reset everything, — reflash FC with Quad firmware.

Is there any bug in the firmware ?
Thank you for your help.
SingleCopter__Param.param (14.5 KB)