Session Cookies not working after update to 3.2.2

[retrofan]

Hello,
first, thanks for your work and for the latest release.
All works fine, except for my Session Cookie JQuery Ajax Script.

I call the following script using a JQuery Ajax Post:

PHP Code:

<?php
    $result = 1;
    session_start();
    if ($_POST['command'] == 'togglesize' ){
        if (@($_SESSION['textsize'] == "normal") ){
            $_SESSION['textsize'] = "big";
        } else {
            $_SESSION['textsize'] = "normal";
        }
        $result = 0;
    }
  /* some more... */
    echo $result;
?>

The request works, but the SESSION cookie is not created and I have no access to the cookie later in my template.php. Did I overwrite some setting while performing the upgrade, oder is there something changed in session handling?

Greetings and thanks for hints!