--- mantisbt-1.1.8/core/bug_api.php     2009-06-08 22:48:31.000000000 +0300
+++ mantis/core/bug_api.php     2010-01-10 18:18:01.000000000 +0200
@@ -1280,6 +1280,22 @@
                                        history_log_event_special( $p_duplicate_id, BUG_ADD_RELATIONSHIP, BUG_HAS_DUPLICATE, $p_bug_id );
                                }
                        }
+
+                       # -------------- CentOS #3931
+                        # Patched by mark@mark.org.il
+                        $query = sprintf("SELECT *
+                                          FROM %s
+                                          WHERE bug_id = %d", config_get( 'mantis_bug_monitor_table' ) , $p_bug_id);
+                        $result = db_query( $query );
+                        $t_count = db_num_rows( $result );
+
+                        for ( $i = 0; $i < $t_count; $i++ ) {
+                                $row = db_fetch_array($result);
+                               bug_unmonitor($p_bug_id, $row['user_id']);
+                               bug_monitor($p_duplicate_id, $row['user_id']);
+                        }
+                        ## END PATCH
+

                        bug_set_field( $p_bug_id, 'duplicate_id', (int)$p_duplicate_id );
                }