subqueues deleted due to racing bug

On a busy website we've been having an issue that about once in a week all subqueues of a certain type were being deleted. When this happened, all subqueues that belong to a queue where that queue has owner='smartqueue_taxonomy' were entirely removed.

This issue is hard to reproduce.

The cause must be:
in /modules/taxonomy/taxonomy.module, function taxonomy_del_term:

 $term = (array) taxonomy_get_term($tid);
(....)
module_invoke_all('taxonomy', 'delete', 'term', $term);

and then in /sites/all/modules/nodequeue/smartqueue.module, function smartqueue_taxonomy($op, $type, $array = NULL)

        case 'delete':
          $tid = $array['tid'];
          if(!$tid) {
            return;
          }
          // Find subqueues that contain this term.
          $result = db_query(
            "SELECT sq.sqid FROM {nodequeue_subqueue} sq
            INNER JOIN {nodequeue_queue} nq ON sq.qid = nq.qid
            WHERE nq.owner = 'smartqueue_taxonomy'
            AND (sq.reference = '%d'
              OR sq.reference LIKE '%%-%d'
              OR sq.reference LIKE '%d-%%'
              OR sq.reference LIKE '%%-%d-%%')",
            $tid, $tid, $tid, $tid
          );
          while ($row = db_fetch_object($result)) {
            nodequeue_remove_subqueue($row->sqid);
          }
          break;
      } 

When in the first block of code the term with that $tid has already been removed the $array parameter in the second block of code will have a bogus value. The SELECT query then selects subqueues to be deleted and uses %d-%% in the selection where %d may be 0, which in our case matches all such subqueues.

We hope we have now solved the issue by changing (inserting into) the start of the second code block as below:

        case 'delete':
          $tid = $array['tid'];
          if(!$tid) {
            return;
          }