Ticket #42395: 42395.3.diff

src/wp-includes/class-wp-customize-manager.php

@@ -1175 +1175 @@
 
                 $changeset_data = array();
                 if ( $this->changeset_post_id() ) {
+
+                        /*
+                         * Don't re-import starter content into a changeset saved persistently.
+                         * This will need to be revisited in the future once theme switching
+                         * is allowed with drafted/scheduled changesets, since switching to
+                         * another theme could result in more starter content being applied.
+                         * However, when doing an explicit save it is currently possible for
+                         * nav menus and nav menu items specifically to lose their starter_content
+                         * flags, thus resulting in duplicates being created since they fail
+                         * to get re-used. See #40146.
+                         */
+                        if ( 'auto-draft' !== get_post_status( $this->changeset_post_id() ) ) {
+                                return;
+                        }
+
                         $changeset_data = $this->get_changeset_post_data( $this->changeset_post_id() );
                 }