A single value from a session cookie isn't getting reset

[Mountain Man]

Hi,

One field value in a session cookie -- The one for firstName -- isn't
changing when I resubmit my form with changed information. When I
disable the cookies my data gets submitted as normal. I'm thoroughly
baffled by this behavior and I'm hoping that it's happening due to a
mistake on my part, rather than being something beyond my control.
Here's my cookie code.

Best wishes,

Mountain Man
<?php
session_start();
session_register('firstName');
session_register('gender2');
session_register('like2');
session_register('population');
?>