Ticket #11358: update-name-in-comment-with-display-name.patch

registration.php

@@ -185 +185 @@
         if ( $update ) {
                 $wpdb->update( $wpdb->users, $data, compact( 'ID' ) );
                 $user_id = (int) $ID;
+                
+                //if the display name has changed, also update the display name in the comments
+                if ($old_user_data->display_name != $data['display_name']) {
+                        $wpdb->update(
+                                $wpdb->comments,                                                                        //comments table
+                                array('comment_author' => $data['display_name']),       //update comment author name
+                                array('user_id' => $user_id),                                           //comment author's user ID
+                                array('%s'),                                                                            //comment author name is a string
+                                array('%d')                                                                             //comment author's user ID is an integer
+                                );
+                }               
+                
         } else {
                 $wpdb->insert( $wpdb->users, $data + compact( 'user_login' ) );
                 $user_id = (int) $wpdb->insert_id;