I have discovered the cause of this problem and I'm working on a fix.
The problem isn't with UBB.threads or with FTM directly, so it was a beast to find. The problem is actually with a security program running on the server that FTM is living on.
We are now running on a highly secure server to help mitigate against future denial of service attacks like the one we experienced a while back.Part of the server's security setting includes a mod_security rule that prevents scripts from running if they contain a URL within the parameter, to guard against people attempting to hijack any redirectors on our server in order to redirect to spam or virus settings. This is also interfering with changing the theme via the popup menu. I'm looking into a fix right now.
