I have experiment a funny bug with session_register in 
this little script :
<?php
//loginf and passfordf go from a form
include("../mysql.inc.php");
session_start();
$login=$loginf;
$password=$passwordf;
print("login : $login password : $password<br>");
session_register("login","password");
print("login : $login password : $password<br>");
?>
the result of printing is the variable $login take the 
value of the variable $password.

If i replace "session_register("login","password");"
by
session_register("login");
session_register("password");

All work fine...

Thank you for your job.

Laurent