Concurrency issue: Paper ID duplication

Hi I am usng the Conference module on a website. And after creation of several papers I found out a lot of duplicated papers IDs.
I've looked a little into the module's code and I think the problem is here:

function conference_nodeapi(&$node, $op) {
  switch ($op) {
      case 'prepare':
        //NOTE: I think this could be a problem when there are simultaneous submissions                                                            
        //Need to check it out                                                                                                                     
        $ctype_paper = variable_get('conference_ctype_paper', 0);
        if ($ctype_paper == $node->type) {
          $paper_id_prefix = variable_get ('conference_default_paperid_prefix', '');
          if (!$node->field_paper_id) {
            $current_max_num = 0;
            $current_max_id = db_result (db_query ("SELECT (field_paper_id_value) FROM {content_type_conference_paper} ORDER BY field_paper_id_val\
ue DESC LIMIT 1"));
            if ($current_max_id == NULL) {
              //since there are no new papers just set up the prefix                                                                               
              $current_max_id = $paper_id_prefix;
            }
            else {
              //Get the max number and then add one and create a new paper                                                                         
              $current_max_num = split ($paper_id_prefix, $current_max_id);
              $current_max_num[1] = intval ($current_max_num[1]) + 1;
            }
            $node->field_paper_id[0]['value'] = $paper_id_prefix.sprintf ("%04d",$current_max_num[1]);
          }
        }
      break;

The check against existing paper ids is done on node prepare. So if more than one person start to create a new paper node, the field used to store paper ID is populated with the same number.
I think that the check should be done on 'insert'.