class CConfig
{
    private $_file = "";
    private $_time = "";

    static $list = array();

    public function __construct($file) 
    {
        if(array_key_exists($file, self::$list)) {
            var_dump(self::$list[$file]);
            return self::$list[$file];
        } else {
            $this->_time = microtime();
            self::$list[$file] = $this;
            return $this;
        }
    }
}

$x = new CConfig("_index.php");
var_dump($x);
echo "<br/>";
$x = new CConfig("_index.php");
echo "<br/>";
var_dump($x);

ожидаемый результат:

object(CConfig)#1 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(21) "0.94009600 1389819843" } 
object(CConfig)#1 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(21) "0.94009600 1389819843" }
object(CConfig)#1 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(21) "0.94009600 1389819843" }

Реальный результат:

object(CConfig)#1 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(21) "0.94009600 1389819843" } 
object(CConfig)#1 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(21) "0.94009600 1389819843" } 
object(CConfig)#2 (2) { ["_file":"CConfig":private]=> string(0) "" ["_time":"CConfig":private]=> string(0) "" }

Где потерялось значение _time или что я упустил?