Try this replacement code as the fix:
Code:
  function zen_get_all_get_params($exclude_array = '', $search_engine_safe = true) {

    if (!is_array($exclude_array)) $exclude_array = array();
    $exclude_array = array_merge($exclude_array, array(zen_session_name(), 'main_page', 'error', 'x', 'y'));
    $get_url = '';
    if (is_array($_GET) && (sizeof($_GET) > 0)) {
      reset($_GET);
      while (list($key, $value) = each($_GET)) {
        if (is_array($value) || in_array($key, $exclude_array)) continue;
        if (strlen($value) > 0) {
          $get_url .= zen_sanitize_string($key) . '=' . rawurlencode(stripslashes($value)) . '&';
        }
      }
    }
    while (strstr($get_url, '&&')) $get_url = str_replace('&&', '&', $get_url);
    while (strstr($get_url, '&&')) $get_url = str_replace('&&', '&', $get_url);

    return $get_url;
  }
Suitable for v1.3.9a thru v1.5.0
Fix included in v1.5.1