rss feed not updating

I recently changed my feed so that it excludes a category by insterting this code (thank you Otto24) in the functions.php file:

//exclude category 12

function limit_feed() {
if (is_feed() && !is_category()) {
query_posts($query_string . "&cat=-12");
}
}
add_action('rss2_head','limit_feed');

//END exclude category 12

Since then, my feed does’t seem to update properly. If you check the feed directly at: http://www.divaknitting.com/blog/?feed=rss2 the latest post from yesterday is missing. Any ideas on what might be causing this?