EDITED Saturday 11/20:
OK, the bug is fixed. I downloaded 1.4.0pre 6 and checked out the problem. It appears that in 1.3.2, a spectral class "Q" star has a particular radius of about 4 km. To cover it with a planet (my black hole), you need to cover it with a sphere having a slightly larger radius. I used 5 km as the radius, and it worked fine.
In Celestia 1.4.0 pre 6, the spectral class "Q" is now given a designation as a "Neutron star". Apparently, its radius has been made larger (10 km). Thus, my 5 km black hole model was inside the star and not visible. When I changed the radius to about 20 km, the black hole appeared fine. Problem solved.
I have uploaded a corrected add-on to motherlode to change my sphere radius from 5 to 20, so that users with 1.4.0 can see it. If you already have the add-on, just open/edit the black_hole_108.ssc file and change the "Radius" to 20. Also, change the "Atmosphere" height in the ssc file to read "4.5" instead of reading "1". Re-save the ssc file and the Black Hole will display fine.
One more thing, however. I use a different star "flare.jpg" image in Celestia. I don't like the default one with the flare spikes, so I redesigned it to have a soft glow, but no spikes. When viewing the Black Hole 108 add-on, the spiky flare that comes with Celestia and appears around it kind of takes away from the reality of the model in my opinion, since the black hole is too dim to have glaring spikes in the radiation around it.
I have uploaded my soft glow flare file to my website. You can get it there. To use it, simply replace the flare.jpg file in Celestia's main texture folder with my version.
Selden, thanks for the input. In the future, I will keep both versions of Celestia on my system.
Enjoy.
Frank