This will also cause the same error:

$iterator = new RecursiveIteratorIterator(new \ArrayObject([]));
Fatal error: Uncaught exception 'InvalidArgumentException' with message 'An instance of RecursiveIterator or IteratorAggregate creating it is required' in /var/www/sando/bin/iteratorBug.php on line 2

InvalidArgumentException: An instance of RecursiveIterator or IteratorAggregate creating it is required in /var/www/sando/bin/iteratorBug.php on line 2


ArrayObject does implement IteratorAggregate:
$  php -r 'var_dump(class_implements("\ArrayObject"));'
array(5) {
  'IteratorAggregate' =>
  string(17) "IteratorAggregate"
  'Traversable' =>
  string(11) "Traversable"
  'ArrayAccess' =>
  string(11) "ArrayAccess"
  'Serializable' =>
  string(12) "Serializable"
  'Countable' =>
  string(9) "Countable"
}

RecursiveIteratorIterator is an iterator over other recursive iterators. As such it needs to be given either (a) a RecursiveIterator or (b) an IteratorAggregate that produces a RecursiveIterator.

ArrayIterator is not recursive, thus the error. Use RecursiveArrayIterator instead.
http://3v4l.org/Ia7qL

ArrayObject is an IteratorAggregate and this bug still presents itself:

$iterator = new RecursiveIteratorIterator(new \ArrayObject([]));

Yes, ArrayObject is an IteratorAggregate, but its getIterator() method does not return a recursive iterator. That's the problem. It has to return a recursive iterator to be valid.

Ok thanks for clearing that up.  I see where what you are getting at. 

This worked just fine: 

class IteratorBug implements IteratorAggregate
{
    public function getIterator()
    {
        return new RecursiveArrayIterator(['foo' => [1,2,3], 'bar' => [1,2,3]]);
    }
}

$iterator = new RecursiveIteratorIterator(new IteratorBug());