That's the designed behavior - after a thread has reached 25 posts, the standard topic review will not be displayed for browsers that do not support the HTML4 / XHHTML1 IFRAME tag. Netscape 4 doesn't support IFRAME, but Netscape 6 does.
Cache fix - create a file called .htaccess in your UBB's noncgi directory. The file needs to contain the following lines:
<FilesMatch *.html>
Header add Cache-control no-cache
</FilesMatch>
Upload the file in ASCII mode.
