Add this after line 168 of reserve.php:
$res->summary = stripslashes($_POST['summary']);
And change line 438 of lib/db/ResDB.class.php to this:
$values = array(0, $res->get_id(), $res->get_summary());
And change line 441 of lib/db/ResDB.class.php to this:
. ' SET is_pending = ? AND summary = ?'
This is untested, so back everything up first.