Description:
------------
Seem to be able to extend instances outside class definition

Reproduce code:
---------------
class one{
 public $vars;
}
$inst=new one;
$inst->newvar="should make error";
print $inst->newvar;


Expected result:
----------------
An error where the class is modified externally to its definition.

Actual result:
--------------
allows instance to be extended willynilly.
Not sure if this is language feature by design - doesnt feel right to my  view of OO.