php __get 函数一个隐藏问题

<?php
/**
 * Copyright (c) 2009
 * All rights reserved.
 * 
 * 名    称：
 * 摘    要：
 * 版    本：1.0
 * @author zhoudan
 * @since 10.03.24 17:06:53
 */


class App{
    public $a = array(1,2,3,4);
   
    function &getA()
    {
        return $this->a;
    }
	
	function p()
	{
		print_r($this->a);
	}
}

class Test{
	
	private $app;
	
	function __get($name)
	{
		if($name === "a")
		{
			$this->a = &$this->app->getA();
			return $this->a;
		}
	}
	
	public function __construct(App $app)
	{
		$this->app = $app;
	}
	
	public function p()
	{
		$a = &$this->a;
		$a[0] = 100;
		//$this->a[0] = 100;
		$this->test();
		print_r($this->a);
	}
	
	public function test()
	{
		$test = &$this->a;
		$test[1] = 100;
	}
}

$app = new App();
$test = new Test($app);

$test->p();
$app->p();

?>