ex:

<?php 
  function &foo(&$v) 
  { return $v;
  }
  class Cl 
  { var $a=5; 
  } 
  $x=&new Cl(); 
  print_r($x);
  $x=&foo($x); 
  print_r($x); 
?>
outputs:
cl Object
(
    [a] => 5
)
cl Object
(
)
but if we change 
  $x=&foo($x); 
  print_r($x); 
to
  $y=&foo($x); 
  print_r($y); 

everything works fine;