Try to go at this url:
http://ip.umbriaforum.com/forum.php
and try to chage style (but only from forum.php page). If you can see some parts of template (navlinks block) are not updated with new style choosed. All works fine if you change styles from index.php page, even if some parts (see calendar block) are not fully updated.
To update all, I have to click on CMS page, and all parts and blocks goes fine. I have check in CMS the navlinks block, but it is not cached. Have you got an idea?