If you simulate a LIDAR instrument over either the Forest or Urban scenes, the trees do not appear to exist. The resulting point cloud appears as though the trees are not even there.
This had to do with how the leaf transmission was configured. The LIDAR radiometry solver imposes strict conservation of energy and the classic radiometry solver (used for the passive simulations of those scenes) preserves some DIRSIG3 era assumptions about the reflectance always being 1-emissivity ... even when transmission is present.
The fix was to return to the extinction description of the leaves which correctly behaves with all the radiometry solvers. In addition, the Forest and Urban scenes were cleaned up to removed unused material descriptions and files.