Quad Virtually finished, last Pixhawk Issue - Mission Planner Experts Please!

[Adamantium]

Hey All

So I';m nearly there with my quad project, will be posting pictures and videos up soon.
But I have one last Issue which isnt making sense to me, and hoped you guys could help please.

So its had a "compass variance" error for a while, and Ive managed to trace it to only happening when I plug the battery in with no USB power (as you would normally). If the pixhawk is prefired up from the usb, then you add power, it green lights no problem. Now heres what I think is why:

When the battery goes in, the retracts lift up and camera gimbal drops down. Thus meaning I cant stand it flat when it does its preflight checks. Once checks are finished, and its failed (usually)/yellow light, the legs come down and the camera comes back up. After this has happened I can flick the switches on the tarais and the gimbal and legs work as they should.

So The question is, how can I stop the automatic movement of the legs and camera on startup?

I tried reversing the channel in MP parameter list but this had no effect whatsoever, on anything.

Here';s where it gets confusing!
Retracts are in Aux1, Camera Gimbal Aux 2. When I set it last this was assigned as RC9 = 27 (Landing Gear) and RC10 = 1 (RC Passthrough). When I come to it now. RC9 is disabled = 0, RC 10 and RC 11 = 1. If i change it back to how it should be, everything stops working (like everything, camera gimbal and all). So I set it back to saved settings and its working as before. :/

Any ideas whats going on here?

My understanding is receiver channels 1-8 are for flight controller motors/escs, therefor AUX channels start at 9 = 1, 10 = 2 etc. Where I get confused is when MP offers both a RC10, and a Ch10_OPT. Why the hell are there two? and why not for all channels?

If it helps, my Taranis is setup as follows:

Ch1 - 4, Throttle/Pitch/Roll/Yaw
Ch 5 - Mode Switch
Ch 6 - Gimbal Pitch
Ch 7 Gimbal Roll
Ch 8 Gimbal Yaw
Ch 9 Landing Gear
Ch 10 Camera Mount
Ch 11 - 13 Not used
Ch 14 Video Feed Switch (Connected Directly to receiver Slot 7)
Ch 15 Lights (Connected Directly to receiver Slot 8)

I know there';s a lot there but this is maddeningly confusing, and if anyone with more understanding of Mission Planner could shed some light that would be amazing!
Cheers

[RawLiquid]

Given your rush of responses I thought I might offer up a suggestion or two, I don';t suppose you have checked your failsafes in the radio???

What I mean is, I use spektrum radios, and with them, the failsafe values are determined by what the channel is set to at bind time, and the behavior can be slightly altered based on the exact sequence during binding, If I remember right, binding normally dictates powering up the receiver with the bind plug in, then removing it before binding. an alternate behavior can be defined by not removing the bind plug.

I have not in particular used the aux channels for anything in quite some time, but I am under the impression that the first 8 channels are intercepted by pixhawk and anything over that is passed through. I will go and do a little looking around and see if anything else comes to mind though.