This happened when I migrated from my old MBP to my new MBP (one broke, so Apple sent me a new one). The old MBP didn't have a corrupted icon, but the new one did. So I even tried copying the preferences pane from the old machine to the new one, and the icon was still messed. I checked the icon in the preferences pane with icon maker or whatever it's called (in the dev tools), and it looks fine.