I applied a more minimal changeset (https://hg.savannah.gnu.org/hgweb/octave/rev/a25b50b9034c) which fixes the issue for the two examples in this report.  This will be a part of the 9.3 release which should be quite soon.

Marking as Fixed and closing report.

Legend markers are handled specially in legend.m and their handles are not visible.  They are simply found with the property markertruesize.

In hdl2struct.m, these need to be added to the regular child lists for the legend, and not marked as special.

These changes seem to work for me:

@@ -62,6 +62,8 @@ function s = hdl2struct (h)
         ## Check for polar plots with special "polar_grid" object
         ## FIXME: A hack to fix bug #62093.
         kids = [kids; findall(h, "tag", "polar_grid")];
+        ## Add legend markers which are normally hidden
+        kids = [kids; findall(h, '-depth', 1, 'type', 'line', '-property', 'markertruesize')];
       endif

       nkids = length (kids);
@@ -131,6 +133,10 @@ function hlist = getspecial (h)
   hlist = [];

   regkids = get (h, "children");
+  ## Add legend markers which are normally hidden to regkids
+  if ( strcmp (get (h, "tag"), 'legend') )
+    regkids = [regkids; findall(h, 'type', 'line', '-property', 'markertruesize')];
+  endif
   ## inline version of allchild() for performance
   set (0, "showhiddenhandles", "on");
   allkids = get (h, "children");

The legend is incorrect when using copyobj to copy a figure.  The legend in the new figure is missing markers.

Test using Demonstration 1 in the Octave Forge documentation.