I'm sorry but we need access to your backend as well. I've tried to access http://www.yoursite.com/administrator but it redirects me back to homepage. Please provide your super users access so that we can have full access to your backend.
May I know how and where to replicate this? I've tried to post a comment as a Guest which doesn't has email and it doesn't get the previous avatar. http://screencast.com/t/x2Hzez7kGFoH . Please advise.
I'm not sure that exactly empty emails are the cause of the problem.
I use gravatar system on site, so it's impossible - when users without emails have avatars.
But they have, and Komento displays avatars from another user.
I've tried to post a comment in my local using zaxavar@gmail.com and I can see that email has a gravatar assigned to it: http://screencast.com/t/l9Ijvc3hQl . Means it didn't get from the previous comment in your site. The gravatar really exists: http://en.gravatar.com/zaxavar