Unfortunate behavior resulting from extending IteratorIterator

output

A: object(A)#1 (2) {
  ["extra":"A":private]=>
  string(18) "not gonna see this"
  ["storage":"ArrayIterator":private]=>
  array(5) {
    [0]=>
    int(1)
    [1]=>
    int(2)
    [2]=>
    int(3)
    [3]=>
    int(4)
    [4]=>
    int(5)
  }
}
extra: not gonna see this


B: object(b)#2 (0) {
}
Notice: Undefined property: b::$extra in /root/blankdir/test.php on line 12
extra: 

test.php

<?php

class A extends ArrayIterator {
	private $extra;
	public function __construct($extra) {
		$this->extra = $extra;
		parent::__construct(array(1,2,3,4,5));
	}

	public function count() {
		var_dump($this);
		echo "extra: {$this->extra}\n";
		return 5;
	}
}

class b extends IteratorIterator {
}



$a = new A("not gonna see this");
$b = new B($a);

echo "A: ";
$a->count();
echo "\n\nB: ";
$b->count();
?>