Update: This is indeed a PCRE bug, Jake was right. This started on the assumption certain keywords make the thread title go blank. After further testing, the issue is related to the number of chars present into thread title. For some reason the node title limit (50 chars) gets somehow intersected with the thread title, only when you view the thread list and only into thread title (compare line 327 with 333): I created a live demonstration of this nasty bug, you can follow the original thread also. Server setup: CentOS 6 64bits minimal install with Nginx 1.2.2, PHP 5.3.17 and MariaDB 5.2.12 Please do not state that you cannot replicate this issue, because is there. Others users reported the same behaviour on their servers.