weird 404

Hi, I’m having this strange problem.
I’m using the changed permalinks and they look like this: /%category%-something/%postname%/ . The problem shows when an user tries to acces a page that doesn’t exist, like /%category%-blabla. He is redirected to the main page but with some weird encoding so none of my czech letters are shown ok. I would like to show the main page allright or to show an 404. My .htaccess looks like this :

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Any help much appreciated.