Non-WP rewrites not saved on a multisite install

[johnbillion]

The following code adds a rewrite rule which is classed as a non-WP rewrite rule because its redirect doesn't begin with index.php, and is stored in the non_wp_rules member variable of the WP_Rewrite class.

function my_rewrite() {
	add_rewrite_rule( 'login/?$', 'wp-login.php', 'top' );
}
add_action( 'init', 'my_rewrite' );

On a single site install, this rewrite rule gets saved directly to the .htaccess file rather than being added to WordPress' internal rewrite array.

On a multisite install, this doesn't happen and the rewrite rule has no effect (probably because once a site is multisite-d WordPress no longer writes to .htaccess). The rule has to be manually added to .htaccess.

Likely introduced in 3.0, reproduced in 3.3 and trunk.