When I turn off the register_globals parameter in php.ini, php seems to loose session tracking.
In the example below, the next page presents nothing except if I turn on the register_globals parameter.

//--- first page
<?php
  session_start();
 
  $toto=2;
  session_register('toto');
?>
<a href="next.php">next</a>

//--- next page
<?php
  session_start();

  echo $HTTP_SESSION_VARS['toto'];
?>