Great - wish I could say the same with importing the tube, but I think I know what is wrong. I also found a way to do the same thing with the basic Alice shapes - will post it when I have more time.

The invisible thing usually isn't even really a bug - it's just that some - but only about half - of the programs leave that parameter blank when you don't use transparency in generating the model - so if you haven't explicitly overridden the default (which I assume you can do but I haven't tried), Alice will guess wrong about half the time. The same is true with the orientation of surface normals (which I think is my problem with the tube).

Jim