A short script:
<?php
  class test_class_2{
        var $name;
        function distort_reality(){
                 echo("Method Called.<br>\n");
                 return;
        }
  }
  $a[] = new test_class_2;
  $a[0]->name = 'Original';
  echo('$b = $a<br>'."\n");
  $b = $a;
  echo("Original contains: {$a[0]->name}<br>\n");
  echo("Copy contains: {$b[0]->name}<br><p>\n");
  echo("Change contents for \$b<br>\n");
  $b[0]->name = 'Copy';
  echo("Original contains: {$a[0]->name}<br>\n");
  echo("Copy contains: {$b[0]->name}<br><p>\n");
  $a[0]->distort_reality();
  echo('Once again, $b = $a<br>'."\n");
  $b = $a;
  echo("Original contains: {$a[0]->name}<br>\n");
  echo("Copy contains: {$b[0]->name}<br><p>\n");
  echo("Change contents for \$b<br>\n");
  $b[0]->name = 'Copy';
  echo("Original contains: {$a[0]->name}<br>\n");
  echo("Copy contains: {$b[0]->name}<br>\n");
?>

The output from the script:

$b = $a
Original contains: Original
Copy contains: Original

Change contents for $b
Original contains: Original
Copy contains: Copy


Method Called.
Once again, $b = $a
Original contains: Original
Copy contains: Original


Change contents for $b
Original contains: Copy
Copy contains: Copy

Basically, if $a is an array of objects and any method of an object is called any subsequent copy of $a becomes linked to the original.  Any change to the copy propagates through to the original.

Configure line:
 './configure' '--with-config-file-path=/usr/local/stronghold/conf' '--with-apxs=/usr/local/stronghold/bin/apxs' '--enable-versioning' '--disable-debug' '--with-zlib' '--with-gd=/usr/local' '--with-gdbm' '--with-db2' '--with-mysql' '--with-xml' '--with-ldap' '--with-cpdflib=/usr/local' '--with-png-dir=/usr' '--with-jpeg-dir=/usr' '--with-tiff-dir=/usr' '--with-xpm-dir=/usr/X11R6' '--enable-sysvshm=yes' '--enable-sysvsem=yes' '--enable-track-vars=yes' '--enable-bcmath=yes' '--enable-memory-limit=yes'

Running as a module under apache 1.3.14