Following diff diminishes most of leak. However, there still some leaks remains.

--- helper-toolbar-common-gtk.c (revision 792)
+++ helper-toolbar-common-gtk.c (working copy)
@@ -88,7 +88,7 @@
 static void
 helper_applet_prop_list_update(gchar **tmp)
 {
-  GtkMenuShell *prop_menu = NULL; /* quiet gcc */
+  static GtkMenuShell *prop_menu = NULL; /* quiet gcc */
   GtkWidget *button;
   int i = 0;
   gchar **tmp2 = NULL;
@@ -137,6 +137,10 @@
          button = gtk_button_new_with_label(tmp2[1]);
          gtk_box_pack_start(GTK_BOX(hbox), button, TRUE, TRUE, 0);
          menu_buttons = g_list_append(menu_buttons, button);
+
+         if (prop_menu) {
+           gtk_widget_destroy(prop_menu);
+         }
           
          prop_menu = (GtkMenuShell*)gtk_menu_new();

Here's another leak
--
          GtkWidget *menu_item = gtk_menu_item_new_with_label(tmp2[2]);
-         g_object_set_data(G_OBJECT(menu_item), "prop_name", g_strdup(tmp2[4]));
+         g_object_set_data_full(G_OBJECT(menu_item), "prop_name",
g_strdup(tmp2[4]), g_free);
          gtk_menu_shell_append(prop_menu, menu_item);

Diff in comment #2 is obvious. So I commited it.
Please audit #1 and investigate other leaks. menu_item is possible culprit.

First patch is not enough to fix all of memory leaks, because prop_menu
may be used more than one times.

I committed fix of leaking by another way, please test rev 814.

I confirmed.
This problem seems to have fixed.