This is very puzzling. You had all "reverse" and that's the way it flew. Now you have ailerons "normal" and it flies like that. If you never changed any servos,wires,ect in the plane or radio then I'd be real curious now to find out which way is "right" for this plane. Anyone else have the Nexstar EP they can check?

I started over a year ago too and have set up many planes on 3-4 transmitters and I did have 1 similar incident where an existing plane mysteriously got the throttle "reversed". I changed it like you did and it works fine ever since. Never did find out why.