Cannot pitch up/down in Jets (it says RMB is already bound when it's not)

Hi,

I use the Right Mouse button for "throttle up / walk forwards".  This is fine for everything apart from Jets. 

For some reason, holding right mouse button in a jet locks the pitch.  I.e. I can't pitch up and down when the RMB is pressed.  It's as if RMB is mapped to something else as well and causes a conflict.

I've tried deleting EVERY SINGLE key mapped to the mouse under the Jets section to ensure there's no conflict, but when i try to then assign the RMB to "Throttle Up" it says that the key is already bound - however there IS NOTHING bound in the Jet's section to RMB other than Throttle Up.

Any help would be much appreciated as I'm totally unable to use the jet right now ☹️

Thanks