[support] Strange behaviour with same page in two different dir

Hi all. I have this file located in / (root of my website) :

<?

require_once './includes/bootstrap.inc'; drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

global $user; print_r($user); $page = "io sono la pagina"; echo theme('page',$page); ?>

And this page works like without problem (the output is my "user" data).

Now I have this page located in /subdir1 (of my website):

<? chdir(".."); require_once './includes/bootstrap.inc'; drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

global $user; print_r($user); $page = "io sono la pagina"; echo theme('page',$page);

?>

But this page does not work like I expect it: the user is anonymous and not my "user logged in". Why this ? Note the the only different is "chdir('..');"

Tnx.