Thanks for the credentials. I created a user associated with the Facebook user that you gave dev permissions to, joined a group and had that action posted to my Facebook timeline.
Here are the changes that I made to resolve the issue:
1. As mentioned, JomSocial was improperly adding some Open Graph tags to the page. In /components/com_community/helpers/head.php, I commented out lines 63 and 73.
2. You were using the Facebook common type 'group'. However, you can't do that, so I created another object called 'JGroup'.
3. Explicitly Shared, Places, etc were not appropriate for the action, so I unset them.
* #2 and #3 were changed in both your Facebook application and in the JFBConnect backend.
I've deleted the user, so the activity log action is no longer present. You should be able to successfully join a group now though, so let me know if you continue to have problems.
-Melissa
Open Graph & Facebook
