I don't think that it is a matter of access rights as I see that iomap.cfg is updated and accepts changes of other cotrollers. It must be an issue with the throttle quadrant itself however I can't find any explanation as it is a common HID controller with no special features - actually the same kind as the joystick.
Here's what I set on the controller page:
and here's what the part within the "plane" section reads for the throttle and mixture controllers (the axis controller reads exactly the values for primary and secondary as in the above picture)
{
"name" : "throttle",
"bindings" : [{"event_name":"Axis2","device_name":"INDEV_HID1","invert":true}]
},
{
"name" : "throttle_up",
"bindings" : [{"event_name":"Insert"}]
},
{
"name" : "throttle_down",
"bindings" : [{"event_name":"Delete"}]
},
{
"name" : "mixture",
"bindings" : [{"event_name":"Aaxis4"},{"event_name":"Axis0","device_name":"INDEV_HID1","invert":true}]
},
{
"name" : "mixture_up",
"bindings" : [{"event_name":"Home"}]
},
{
"name" : "mixture_down",
"bindings" : [{"event_name":"End"}]
},
Apart from the strange entries in the first line of each the throttle and the mixture controller there are also no entries for the primary controller axis as seen in the picture above. Maybe this gives you a clue what happens here?