Curious rotor rust problem

[SDGTP99]

Ohkay, so the inside diameter of my right rear rotor is rusted. There's about a 1" wide ring of rust starting on the inside of the rotor and expanding outward. I thought this problem had been caused by a crooked caliper piston. So I replaced the caliper. It's been a month & that rust ring is still there. Any thoughts comments or suggestions would be greatly appreciated.

 

[The Guz]

Any photos so we know exactly what it is?

 

[SDGTP99]

I replaced the pads and the ring of rust went away. Obviously the pads were worn at an angle because of the crooked caliper piston. I should have replaced the pads when I replaced the rotor. Problem solved.