Here are two scripts that operates on referenced objects. make.php creates object $b with reference to object $a as argument.

After serialize/unserialize show.php checks if the reference still exists.

PHP 4.0.1pl1 lost references.
PHP 4.0.4pl1 segfaults on show.php
PHP 4.0.5    segfaults on show.php and(!) sometimes on make.php

Config line:
./configure --with-pgsql=shared --with-apxs --sysconfdir=/etc --prefix=/usr \
--localstatedir =/var --with-config-file-path=/etc/httpd/conf/ \
--with-gettext=/usr/share/gettext

make.php:
<?
class ClassA {
 var $arg_a;
};

class ClassB {
 	var $arg_b;
 
 	function ClassB(&$a) {
		$this -> arg_b = &$a;
	}
};

session_start();
session_destroy();
session_register("b");
session_register("a");

$a = new ClassA();
$a -> arg_a = 4;
$b = new ClassB($a);
echo "done. Click <a href=\"show.php\">here</a>";
?>


show.php:
<?
class ClassA {
 var $arg_a;
};

class ClassB {
 	var $arg_b;
 
 	function ClassB(&$a) {
		$this -> arg_b = &$a;
	}
};

session_start();
$a -> arg_a = 6;
echo $b -> arg_b -> arg_a;
?>