References to $this are randomly wrong during __wakeup.
I am keeping track of all objects in a global $objs.

global $objs;
$objs[] =& $this;

during __wakeup causes $objs[] to gain an element that matches some random OTHER variable in my script (an integer I was using somewhere, or an array I had somewhere else)

Unforunately I cannot reproduce this on a simple script, but here is the essence of what I am doing:

<?
$objs = array();

class O {
  function __wakeup() {
    global $objs;
    $objs[] =& $this;
  }
}

class X extends O {
  var $a = 213;
  var $b = 'hello';
}

$x = new X();
$y = serialize($x);
$z = unserialize($y);

var_dump($objs);
?>

^^ the above script works perfectly, but in a more complex script doing the same thing, it ends up putting a reference to a totally different variable into $objs.