Here a small script to reproduce:

<?php
class A extends ArrayIterator
{
protected $aa;
public function construct()
{
$this->aa = 302;
parent::construct(array());
}
}

$a = new A();
print_r($a); // put breakpoint here
?>

The script's output is:
A Object
(
[aa:protected] => 302
[storage:ArrayIterator:private] => Array
(
)

)

I have tested it in Xdebug Version 2.1.4 and 2.2.0

CLosing as a duplicate of 0000686.

This wasn't actually a duplicate. Closing it now though, as it's fixed for Xdebug 2.2.3 and 3.0dev. Thanks for the report!