After update of mantis when bug_assign is called on php side it automatically creates empty note although even comment inside function states that it only creates note when some is supplied. Maybe missing if?

# Add bugnote if supplied ignore false return
if ( ! is_blank($p_bugnote_text) ) {
    $t_bugnote_id = bugnote_add( $p_bug_id, $p_bugnote_text, 0, $p_bugnote_private, 0, '', null, false );
    bugnote_process_mentions( $p_bug_id, $t_bugnote_id, $p_bugnote_text );
}