I also have this problem of using Jetpack 2.2 and using the Publicize feature to Facebook it keeps using this image:
https://1.gravatar.com/avatar/3c37792db0ce671809b94f5365aba2b7?s=80&d=&r=G
I want it to display either the authors avatar or images within the blog, if I paste the URL manually into Facebook it works fine and I can select either the author avatar or images within the post.
Why is Facebook grabbing this default avatar?