Ticket #13481: 13481.diff

wp-includes/taxonomy.php

@@ -1626 +1626 @@
                         if ( false === $wpdb->insert( $wpdb->terms, compact( 'name', 'slug', 'term_group' ) ) )
                                 return new WP_Error('db_insert_error', __('Could not insert term into the database'), $wpdb->last_error);
                         $term_id = (int) $wpdb->insert_id;
+                } elseif ( is_term( (int) $term_id, $taxonomy ) )  {
+                        // Same name, same slug.
+                        return new WP_Error('term_exists', __('A term with the name provided already exists.'));
                 }
         } else {
                 // This term does not exist at all in the database, Create it.