PHP stops embeding the session id into URLs after calling virtual().

Example (switch off your cookies):
--------------------------------------
session_start();
session_register('count');
$count++;
echo $count."<br>";

<A HREF="example.php">link 1</A>
<?virtual("/virtual.html");?>    
<A HREF="example.php">link 2</A>
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First link will be example.php?PHPSESSID=7a85d47f8d5e7c96c579
but second link will be only example.php

If you comment virtual("/virtual.html") everithing will go on fine.