Description:
------------
__autoload() function causes data corruption when using inheritance. In my example, the value of $foo->instance is 2 and SHOULD BE 1 !
In test.php, if I comment the include_once of autoload.php and uncomment the include_file of classes, the value of $foo->instance is correct (=1). 
Why ? Normally, there is no difference between autoload and explicit class file inclusion ?

Reproduce code:
---------------
To test the bug, you need four files.
test.php :
<?php
include_once "autoload.php"; 
//include_once "test2.php";
//include_once "test2_child.php";

$foo = new test_oop();
$child = new test_oop_child();
echo $foo->instance . "<br>";
echo $child->instance . "<br>";
?>

test2.php :
<?php
class test_oop {
	private static $instances = 0;
	public $instance;
	
	public function __construct() {
		$this->instance = ++self::$instances;
	}
	 
} // class
?>

test2_child.php :
<?php
include_once "autoload.php"; 

class test_oop_child extends test_oop {
	 
} // class
?>

autoload.php :
<?php
function __autoload($className) {
	require_once $className . ".php";
} 
?>

Expected result:
----------------
$foo->instance = 1

Actual result:
--------------
$foo->instance = 2