.htaccess rules don't work with Plain

[sebastian.pisula]

If I use "Plain Url Style" in Permalink Settings then I can't add custom rules .htaccess from mod_rewrite_rules filter. I think that this is bug.

For example:

<?php
function uploads_from_remote_server( $rules ) {
        $rules = "<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule wp-content/uploads/(.*) http://example.com/wp-content/uploads/$1 [NC,L]
</IfModule>\n\n" . $rules;

        return $rules;
}

add_filter( 'mod_rewrite_rules', 'uploads_from_remote_server' );

This filter not working in Plain Url Style but should.