I'm unsure what you're seeing, but it seems to work for me. I just posted a comment on articles2/news2/86-joomla-seo-low-performance
I'm attaching an image of me in a private browsing session, so I'm not logged into Facebook, but I can still see the comment:
If you can see it, then it is working right. If you're posts don't show up, please check your Facebook privacy settings as there may be some option to hide your comments from all other users. You may also want to try from various Facebook accounts to see if there's some pattern to when it does and doesn't work.
Thanks,
Alex