if a figure is filed with a surface and 2 other quiver3 plots for example, shading returns the error.

error: octave_base_value::array_value(): wrong type argument 'cell'
error: get: H must be a graphics handle

It happens in this part of shading line 66 to 82

hlist = [];
  kids = get (hax, "children");
  while (! isempty (kids))
    types = get (kids, "type");
    hlist = [hlist; kids(strcmp(types, "patch"))];
    hlist = [hlist; kids(strcmp(types, "surface"))];
    parents = kids(strcmp (types, "axes"));
    hglist = kids(strcmp (types, "hggroup"));
    for i = 1 : numel (hglist)
      props = get (hglist(i));
      if (! isfield (props, "levelstep"))
        parents(end+1) = hglist(i);
      endif
    endfor
    if
    kids = get (parents, "children");
  endwhile

from what i have been able to figure out, for 2 or more quiver3 plots, 2 hggroups are created and found in

hglist = kids(strcmp (types, "hggroup"));

The for loop puts them in parents making parents a array
and get returns a cell of "children"(graphics handles)? to kids.
At the beginning of the while loop
verbatim+
types = get (kids, "type");
-verbatim-
fails because get cant handle a cell, only arrays of graphics handles?