problem with scm_set_object_property_x

[Bill Schottstaedt <bil at ccrma dot stanford dot edu>]

It's not clear to me how to use scm_set_object_property_x;
I'm trying to set the documentation property on the object's
property list for a help system (in my sound editor);
set-object-property! works fine in scheme, but the C
side using scm_set_object_property_x
seems to do nothing.  The similar sequence using
scm_set_procedure_property_x works fine.  In
the procedure case I'm using something like:

scm_set_procedure_property_x(
  gh_new_procedure(...),
  scm_string_to_symbol(gh_str02scm("documentation")),
  gh_str02scm("some text"));

which gives me a property list with arity and documentation.
In the object case:

scm_set_object_property_x(
  gh_define(...),
  scm_string_to_symbol(gh_str02scm("documentation")),
  gh_str02scm("some text"));

but the object's property list remains empty. I also tried
to use scm_set_object_properties_x here, and screwed around
with the thing returned by gh_define, all to no avail.