Chris,
Some out of bounds clipping I noticed while viewing a model in Celestia 1.2.2...
This is a borrowed model of Space Station V...
http://cybermindtraveller.freewebspace.com/pics/clipping.jpg
And as you can see it should look like this...
http://cybermindtraveller.freewebspace.com/pics/clipping2.jpg
Might this be the same culprit of the vanishing stars?
<edit> I may be reaching here, but I think I may have it...You render the stars using a mesh maybe? and the outer edges are being clipped due to your mapping being a smaller area???