Thanks Jared and apologies for wasting your time -- but I probably would not have figured it out with Chris and your help.
Unfortunately, I will be out of town for 3+ weeks but I'll make whatever progress I can without access to the mount. It is hard to imagine it is a firmware issue because others would presumably be facing the same issue. That leaves hardware, but that seems a long shot too.
I'll post back here when it gets all sorted out.
Richard