Sorry, correctly this is about RecursiveArrayIterator::getChildren, and a more proper

Test script here:
---------------------------

function example() {
    $array = array (
            'a' => array(
                    'a_1' => 'a 1 text',
            ),
    );

    $array_object = new ArrayObject( $array, 0, "RecursiveArrayIterator"  );
    $iterator     = new RecursiveIteratorIterator( $array_object->getIterator(), RecursiveIteratorIterator::SELF_FIRST );

    foreach( $iterator as $key => $current ) {
var_dump( $iterator->getInnerIterator() );

        //if( $key == 'a' ) {
var_dump( get_class($iterator->getInnerIterator() ));
var_dump( $iterator->getInnerIterator()->getChildren() );
        //}
    }
}

example();

getInnerIterator()->getChildren() => 'a 1 text'

why this is a bug?

I am using 14 Mar 2012, PHP 5.4.13, and running the test script without exception handling. This is the result:

[15-Mar-2013 18:06:44 UTC] RecursiveArrayIterator

[15-Mar-2013 18:06:44 UTC] PHP Fatal error:  Uncaught exception 'InvalidArgumentException' with message 'Passed variable is not an array or object, using empty array instead' in [...]
Stack trace:
#0 [internal function]: ArrayIterator->__construct('a 1 text', 67108864)

On the screen seems everything is OK, I can see the var_dump result also, but in the debug.log file there is a PHP error message.

It is illegal to call getChildren() if hasChildren() is not true, as is the case here. The operation is ill-defined, and that's why you get an exception.