Description:
------------
When ArrayObject::offsetSet() method stores a new value into an array,
I expect ArrayObject to change only the array which is given as a constructor parameter.

However, if the array is copied from another array and unchanged,
ArrayObject will also change the another array.

I thought it was a "copy-on-write" problem.

thank you for any help
Please excuse my English, it isn't very good.

Reproduce code:
---------------
$base = array('key' => 'old value');

$copy = $base;
$ao = new ArrayObject($copy);
$ao['key'] = 'new value';

echo '$base["key"] = ', $base['key'], "\n";
echo '$copy["key"] = ', $copy['key'], "\n";
echo '$ao["key"] = ', $ao['key'], "\n";

Expected result:
----------------
$base["key"] = old value
$copy["key"] = new value
$ao["key"] = new value

Actual result:
--------------
$base["key"] = new value
$copy["key"] = new value
$ao["key"] = new value