Description:
------------
If i use expression like
$a = $b = $c = $d;

where $b or $c determined as class extends ArrayObject, then
ArrayObject::offsetGet method do not call.

It may be only if above expression interpreted as
$a = $d;
$b = $d;
$c = $d;

Test script:
---------------
class foo extends ArrayObject{
  function offsetGet($index){return 'Ok';}
}
$o = new foo();
$a = $o[1];
$b = ($o[1] = 'Fail');
echo $a,$b;
//Output: OkFail

//but if

$o[1] = 'Fail';
$b = $o[1];
echo $a,$b;
//Output: OkOk