The following code is executed every time a report is viewed :

// Upgrade any attempts that have not yet been upgraded to the
// Moodle 1.5 model (they will not yet have the timestamp set)
if ($attempts = $DB->get_records_sql("SELECT a.*".
" FROM

a,

s".
" WHERE a.quiz = ? AND s.attempt = a.uniqueid AND s.timestamp = 0", array($quiz->id))) {
foreach ($attempts as $attempt)

}

It is in mod/quiz/report.php.

I think it needs to be removed from HEAD and can possibly be removed from 1.9 and 1.8 too?