Recent posts plugin is displaying posts from private blogs?!

Hi! I'm using Recent Posts to display global recent posts from all sites - but it is also showing posts from private blogs...
We have blogs made private by selecting "allow only registered users to see this site" (a feature of your own Multisite Privacy-plugin) or smth along those lines.
But private posts showing up on our front page is obviously a problem.
Is there a parameter I can set to exclude those blogs (or must they be excluded from the post indexer? If so, how?)