Session, register_globals, $HTTP_SESSION_VAR

[si]

Session, register_globals, $HTTP_SESSION_VAR

sess.php
<?
$var_name = 'TEST_VAR';

session_register($var_name);

if (isset($HTTP_SESSION_VARS[$var_name])){
$HTTP_SESSION_VARS[$var_name] ++;
}else{
$HTTP_SESSION_VARS[$var_name] = 0;
}

echo "\$HTTP_SESSION_VARS[$var_name] : ".$HTTP_SESSION_VARS[$var_name];
?>

Результат

----------------------------------------
если register_globals = On
----------------------------------------
всегда : $HTTP_SESSION_VARS[TEST_VAR] : 0


----------------------------------------
если register_globals = Off
----------------------------------------
reload : $HTTP_SESSION_VARS[TEST_VAR] : 0
reload : $HTTP_SESSION_VARS[TEST_VAR] : 1
reload : $HTTP_SESSION_VARS[TEST_VAR] : 2
....


Вопрос : Почему ?