Description:
------------
Deleting an index in ArrayObjet also delete it from the original array *if and only if* ArrayObject was not modified.

This may introduce bugs (unexpected deletion in the original array).



Note: if modification of the original array is wanted behaviour, then we have the opposite bugs :
- documentation does not says that the array in ArrayObject constructor is passed as reference
- I we modify the value of some entry in ArrayObject, the the relation between ArrayObject and the original array is lost 

Reproduce code:
---------------
<?php

$array = array('foo' => 'bar') ;
$object = new ArrayObject( $array ) ;


// uncomment this for opposite behaviour 
// and loose the reference between $object and $array
// $objet['foo'] = 'hello' ;


unset($objet['foo']);
var_dump( $array ) ;

Expected result:
----------------
array(1) { ["foo"]=>  string(3) "bar" }

Actual result:
--------------
array(0) {  }