Just discovered what I'm pretty sure is a bug with the new URL rewrite rules:
http://forums.phpfreaks.com/topic/268690-problem-in-connecting-to-sql-server-2008-by-php/unread/
That link gives me the default ngnix 404 page, as pasted below. Even I try to remove the /unread/ part it still shows the below 404 error, and if I try to remove the -php bit the script identifies the correct thread, and redirects me to the above URL anyway. If I remove the entire title, and leave only the topid ID, I get the forum "Can't find this thread" message.
Considering that the keyword seems to be the "php" at the end of the title, I suspect an incorrect quantifier or faulty boundary check.
<html>
<head><title>404 Not Found</title></head>
<body bgcolor="white">
<center><h1>404 Not Found</h1></center>
<hr><center>nginx</center>
</body>
</html>