Busa found this bug but has trouble explaining it as English is not his native language. When object self shadow is set to on, the specularity reflections on a skin switch 180 degrees in the horizontal plane.
To illustrate what I mean imagine you are looking down on a plane on the runway which is facing north and the sun is to the west. With object self shadow set to off the highlights appear on the left side of the aircraft and the shadow stretches out to the right, which is correct. However when object self shadow is set to on the highlights switch to the right side of the aircraft, yet the shadow stays on the right. The highlights are only reversed in the horizontal plane, not the vertical.
This bug also causes the highlight on the spinner to bounce up and down when the engine is running.
There are various example screenshots shown in
this thread in the skins forum.
