I have the following .htaccess file in my web directory for my Symfony2 installation:
RewriteEngine On
RewriteCond %{R
When you write RewriteCond %{REQUEST_FILENAME} !-f
you say "Don't change real files... they should still be reachable." If you remove that, it should work.
The reason for it allowing that is some frameworks let you use http://site.tld/script.php/abc=123&def=456 style of links.
If you want it to allow filenames except app.php, you could add that as another RewriteCond
.