--- a/scripts/plot/legend.m
+++ b/scripts/plot/legend.m
@@ -119,13 +119,20 @@
     ca = gca ();
   endif
 
-  if (strcmp (get (ca, "tag"), "plotyy"))
-    plty = get(ca, "userdata");
-    if (isscalar (plty))
+  if (ishandle (ca) && isprop (ca, "__plotyy_axes__"))
+    plty = get (ca, "__plotyy_axes__");
+    if (isscalar (plty) && ishandle (plty))
       ca = [ca, plty];
-    else
+    elseif (iscell (plty))
       ca = [ca, plty{:}];
+    elseif (all (ishandle (plty)))
+      ca = [ca, plty(:).'];
+    else
+      error ("legend.m: This should not happen. File a bug report.")
     endif
+    ## Remove duplicates while preserving order
+    [~, n] = unique (ca);
+    ca = ca (sort (n));
   endif
 
   if (nargin > 0 && all (ishandle (varargin{1})))

--- a/scripts/plot/plotyy.m
+++ b/scripts/plot/plotyy.m
@@ -79,7 +79,7 @@
     ca = get (f, "currentaxes");
     if (isempty (ca))
       ax = [];
-    elseif (strcmp (get (ca, "tag"), "plotyy"))
+    elseif (ishandle (ca) && isprop (ca, "__plotyy_axes__"))
       ax = get (ca, "__plotyy_axes__");
     else
       ax = ca;
@@ -209,25 +209,21 @@
   addlistener (ax(1), "plotboxaspectratiomode", {@update_position, ax(2)});
   addlistener (ax(2), "plotboxaspectratiomode", {@update_position, ax(1)});
 
-  ## Tag the plotyy axes, so we can use that information
-  ## not to mirror the y axis tick marks
-  set (ax, "tag", "plotyy");
-
-  ## Cross-reference one axis to the other in the userdata
-  set (ax(1), "userdata", ax(2));
-  set (ax(2), "userdata", ax(1));
-
   ## Store the axes handles for the sister axes.
-  try
+  if (ishandle (ax(1)) && ! isprop (ax(1), "__plotyy_axes__"))
     addproperty ("__plotyy_axes__", ax(1), "data", ax);
-  catch
+  elseif (ishandle (ax(1)))
     set (ax(1), "__plotyy_axes__", ax);
-  end_try_catch
-  try
+  else
+    error ("plotyy.m: This shouldn't happen. File a bug report.")
+  endif
+  if (ishandle (ax(2)) && ! isprop (ax(2), "__plotyy_axes__"))
     addproperty ("__plotyy_axes__", ax(2), "data", ax);
-  catch
+  elseif (ishandle (ax(2)))
     set (ax(2), "__plotyy_axes__", ax);
-  end_try_catch
+  else
+    error ("plotyy.m: This shouldn't happen. File a bug report.")
+  endif
 endfunction
 
 %!demo

--- a/scripts/plot/private/__go_draw_axes__.m
+++ b/scripts/plot/private/__go_draw_axes__.m
@@ -40,10 +40,16 @@
     gnuplot_term = __gnuplot_get_var__ (axis_obj.parent, "GPVAL_TERM");
 
     ## Set to false for plotyy axes.
-    if (strcmp (axis_obj.tag, "plotyy"))
-      ymirror = false;
-    else
-      ymirror = true;
+    ymirror = true;
+    if (isfield (axis_obj, "__plotyy_axes__"))
+      if (all (ishandle (axis_obj.__plotyy_axes__)))
+        ymirror = false;
+      else
+        h = axis_obj.__plotyy_axes__;
+        h = h(ishandle (h));
+        h = h(isprop (h, "__ploty_axes__"));
+        rmappdata (h, "__plotyy_axes__")
+      endif
     endif
 
     nd = __calc_dimensions__ (h);

--- a/src/gl-render.cc
+++ b/src/gl-render.cc
@@ -849,7 +849,7 @@
   double ypTickN = props.get_ypTickN ();
   double zpTickN = props.get_zpTickN ();
 
-  bool plotyy = (props.get_tag () == "plotyy");
+  bool plotyy = (props.has_property ("__plotyy_axes__"));
 
   // Axes box
 
@@ -1074,7 +1074,7 @@
       int wmax = 0, hmax = 0;
       bool tick_along_z = nearhoriz || xisinf (fx);
       bool mirror = props.is_box () && ystate != AXE_ANY_DIR
-                    && (props.get_tag () != "plotyy");
+                    && (! props.has_property ("__plotyy_axes__"));
 
       set_color (props.get_ycolor_rgb ());