[PHP]实体类基类和序列化__sleep问题

<?php

class Sina_Data_Object
{
    protected $data = array();
    private $changes = array();
    private $newFlag = true;
    public function __construct($data = array()){
        if (empty($data)) {
            $this->newFlag = true;
        } else {
            $this->newFlag = false;
            foreach ($data as $k => $v) {
                    $this->data[$k] = $v;
            }
        }
    }

    public function __isset($name){
        return isset($this->data[$name]);
    }

    public function __get($name){
        if(!array_key_exists($name, $this->data)){
        	return null;
        }
        return $this->data[$name];
    }

    public function __set($name, $value){
        $this->data[$name] = $value;
        if (!$this->newFlag) {
            $this->changes[$name] = $value;
        }
    }

    public function __sleep(){
        return array('data');
    }

    public function toArray(){
        return $this->data;
    }

    public function isNew(){
        return $this->newFlag;
    }

    public function clearNewFlag(){
        $this->newFlag = false;
    }

    public function isModified()
    {
        return (!empty($this->changes));
    }

    public function getChanges()
    {
        return $this->changes;
    }

    public function clearChanges()
    {
        $this->changes = array();
    }      
}
class Setting extends Sina_Data_Object{
	const STATUS=1;
	public $other='aaa';
	public function __construct($data=array()){
		parent::__construct($data);
	}
}
//初始化对象
$data=array('user'=>'taoshihan');
$setting=new Setting($data);
//动态增加属性
$setting->age=100;
var_dump($setting);
/*
object(Setting)#1 (4) {
  ["other"]=>
  string(3) "aaa"
  ["data":protected]=>
  array(2) {
    ["user"]=>
    string(9) "taoshihan"
    ["age"]=>
    int(100)
  }
  ["changes":"Sina_Data_Object":private]=>
  array(1) {
    ["age"]=>
    int(100)
  }
  ["newFlag":"Sina_Data_Object":private]=>
  bool(false)
}

*/

//动态改变初始化的字段
$setting->other='bbbb';
//序列化对象
$serializeSetting=serialize($setting);
//反序列化对象
$setting2=unserialize($serializeSetting);
var_dump($setting2);
/*
object(Setting)#2 (4) {
  ["other"]=>
  string(3) "aaa"   ########反序列化回来这里还是aaa
  ["data":protected]=>
  array(3) {
    ["user"]=>
    string(9) "taoshihan"
    ["age"]=>
    int(100)
  }
  ["changes":"Sina_Data_Object":private]=>
  array(0) {      ##########change属性里面的数据没有序列化进去
  }
  ["newFlag":"Sina_Data_Object":private]=>
  bool(true)      #########反序列化回来这里是true
}

*/