function _phpbb2drupal_check_tables() causes theming errors

No idea what, but it seems there is a bug in the following code, which shows errors in the pages calling this function:

function _phpbb2drupal_check_tables( $tables = array(), $db = 'default' , $prefix = 1) {
  _phpbb2drupal_db_connect() ;
  db_set_active($db);

  $out['html'] = '<ul>';
  $out['result']= 1;
  foreach ($tables as $table) {
    if ($prefix) {
      $table = db_prefix_tables('{'. $table .'}');
    }  
    if ($GLOBALS['db_type'] == 'pgsql') {
      // adapt from db_table_exists in database.pgsql.inc
      $result = (bool) db_result(db_query("SELECT COUNT(*) FROM pg_class WHERE relname = '%s'", $table));
	}
	else {
      // adapt from db_table_exists in database.mysql.inc
      $result = (bool) db_fetch_object(db_query("SHOW TABLES LIKE '%s'", $table));
    }
    if ($result) {
      $out['html'] .= '<li>'. t('Table %table: OK!', array('%table' => $table)) .'</li>';
    }
    else {
      $out['html'] .= '<li><span class="marker">'. t('Table <strong>%table</strong> does not exist!', array('%table' => $table)) .'</span></li>';
      $out['result']= 0;
    }
  }
  $out['html'] .= '</ul>';
  db_set_active('default');
  return $out;
}