Description:
------------
ob_start (); can't register CLASS method as a callback function.

Reproduce code:
---------------
<?
class test
{
  function test () //constructor
  {
    ob_start ("$this->callback"); //or simply "callback"
    echo 'Some output.';
    echo ob_get_clean ();
  }
  
  function callback ($info) //this function isn't called
  {
    return $info.' stuff';
  }
}

$tmp = new test;
?>

Expected result:
----------------
callbackfunction (class method) to be called;

Actual result:
--------------
It's not called :/