In 2012, try pulling the highlights way down. You may have to compensate by adjusting exposure, shadows, and whites. I do a lot of sun-in shots and this usually does the trick. I get the banding when I use HDR and push the highlight recovery too far. If I watch it, I don't have nearly as much problem. I assume your shot was not HDR, in which case I don't know what causes the banding except that it might be the nature of the beast at those high exposure levels. You know you have pushed the recovery too far if you start seeing narrow dark bands between the very light areas.
I find I have to do a lot of manual touch up of the sun. Techniques include adding color, adding saturation, smoothing out banding and bad flare with the stamp tool used in light and dark modes at low opacities. This is relatively too complicated to explain fully here
My problem is that I can rarely get an exposure with a near full sun which is not blown out to white. I get a small white disk which is the sun, surrounded by the colors of the sunset. This white sun does not look right so I select that area with selective color and the use a color fill adjustment layer to fill that area with a yellow (about 60ish degrees on the color picker). The color should be full saturation and brightness and will look terrible until you take down the opacity until you get a nice very light yellow which blends with the rest of the sky. Then I use the techniques above to refine. I grabbed some quick examples to show what I mean, before and after.
Larry