After struggling almost one week to find the cause for my not entirely working Permalinks on this WordPress installation, I finally found the cure on the WordPress Codex. I already read this page about five times and I just can’t tell how this one paragraph could always slip away… anyway the solution is rather simple.
As I’m a decently paranoid Server Admin I once changed the way Apache reports it’s server software. This poses some troubles with WordPress which checks to see if the host is running Apache or IIS to determine wether to write a .htaccess file with some mod_rewrite rules or not. As WordPress can’t find out on it’s own on my host I just had to help it a little
In wp-includes/vars.php on line 40 is the check for the hosting webserver, I changed the entire line to read
$is_apache = 1;
After this small modification Worpress happily updatet the .htaccess file with the apropriate mod_rewrite rules (given the file permissions are correct on the server).
One small sidenote: If you are using FAlbum and have “friendly urls” enabled you have to make sure that the rewrite rules made by FAlbum are above the ones from WordPress.