Excellent: Your server is running PHP version 5.2.4-2ubuntu5.26 and MySQL
version 5.0.96 which will be great for WordPress 3.2 onward.
Yes i use XCache on my Webserver and WP-Super-Cache as Plugin, disabling the plugin didn’t help.
With the work-around $occurrences = false; it now seems to work!
Let me know i you need additional testing or information for further development. Thanks a lot for the fast help!