OK, curious.
I try it with my few remaining custom Lisp routines, and it doesn't work with those.
I try it with the SincpacC3D routines (which use .NET), and it works fine with those.
So it's possible that old Lisp routines need to be modified to work with this feature.
The only weird thing I noticed is that I seem to get different behavior in different drawings. For example, I tried using the SGRD command in one drawing, and it let me select point objects, and everything worked fine. I tried using it in another drawing, and it still worked, but it asked me to verify the elevation for every point after I selected it. It always got the elevation from the point I selected, but then it gave me a prompt asking me to "Specify elevation or [Grade/sLope/sYstem/Surface]" for each point. Simply hitting return at that prompt used the point elevation. But in the first drawing, I didn't get that prompt at all. Not sure why it worked differently in one drawing than in the other... Some obscure setting hidden somewhere in Civil-3D...? I seem to vaguely remember some sort of setting that might be responsible, but can't remember exactly what it was...