gift_certificates.php as shown has three obsolete settings used in Zen Cart v1.2.x
$left_corner = false;
$right_corner = false;
$right_arrow = false;
but is missing the current setting for
$title_link = false;
Thus, $title_link remains from the previous sidebox's setting. In this case, it contains the value set in /includes/modules/sideboxes/reviews.php:
$title_link = FILENAME_REVIEWS;

So tpl_box_default_left/right.php does this:
PHP Code:
  if ($title_link) {
    $title = '<a href="' . zen_href_link($title_link) . '">' . $title . BOX_HEADING_LINKS . '</a>';