I have had this problem since I upgraded to WP2. Nobody seems to know what the cause is.
I don’t have Livesearch installed.
I have disabled all plugins, and still I don’t get a notification email when a comment is posted. I know the site can send emails (password request works), so it’s not that.
Could it be a permissions thing?
You are lucky to be receiving notification emails at all. Since upgrading to WP2, I haven’t had a single one. And no-one appears to know why.