<?php
$test2 = new cl2();

class cl1 {
  var $test = 'a';
  function cl1() {
    global $test2;
    $test2->change($this);
  }
  function change() {
    global $test2;
    $test2->change($this);
  }
}

class cl2 {
  var $ref;
  function change(&$obj) {
    $this->ref = &$obj;
    $this->ref->test = 'b';
  }
  function change_new() {
    $this->ref->test = 'c';
  }
}

$testobj = new cl1();
echo $testobj->test; // echoes 'b'
$testobj->change(); // uncomment and see!
$test2->change_new(); // echoes 'b' (not c)!!?
echo $testobj->test;

?>