Rewrite-Rules not working on a vhost, everything goes to index.php

Question

after setting up the wordpress htaccess rules in my vhost, i was unable to enter the wp-admin area. I was always redirected to the frontpage of my wordpress instance.

The rewriting itself worked on the mainpage. All links worked so far, but the admin area remains without any access.

Rewrite rules used:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

Personally i dont know where to start looking, im even unable to find that problem over google, which is kinda rare - maybe someone over here knows where the problem is to be located.