I don't know if lua is "officially" available, but since it is enabled...
When I use the script menu to run the script tour-system.celx (freshly downloaded from SourceForge) after Celestia has started and has been displaying Io, no surface textures are loaded while the script is running. Mercury looks like a blank white sphere, for example.
Also, 3DS models like the ISS are invisible. I can't tell if the models or just the textures are missing.
If I visit an object first with a manual GoTo, the surface texture for that object is loaded and it is visible when the script is subsequently run, but other surface textures still are not loaded when the script needs them.
This bug was not previously present.
System:
256MB 500MHz P III, WinXP Pro SP1
128MB GF4 Ti 4200, Detonator 43.45, OpenGL 1.4.0
Celestia v1.3.1p3