Went through my n+1 installation of my preferred wiki, dokuwiki on a Debian server and for the first time run into a small error, a warning actually, that would systematically be displayed on the wiki page header:
Warning: mb_strrpos() [function.mb-strrpos]: Empty haystack in /../../inc/pageutils.php line 142
Warning: mb_strrpos() [function.mb-strrpos]: Empty haystack in /../../inc/pageutils.php line 155
The error was there whether I used aptitude or manual install and I couldn’t find anything online or in the bug tracker about it. Finally went under Dokuwiki IRC channel and with the help of “Chris–S” narrowed down the problem to either mb_string overloading or stricter error checking.
The fix? Changing:
mbstring.func_overload = 7
mbstring.func_overload = 0
in php.ini and restarting Apache. This is a system wide change, there is also a way to change it per site using a .htaccess file. Hope that helps someone.