I'm having this issue on several sites with the Social plugin installed.
When not logged in, if a user tries to authenticate with Facebook or Twitter, after authentication the auth window closes, and it should refresh showing the user logged in and a comment form, but it doesn't.
This occurs on sites with different themes and plugins. The plugin works as expected on a much smaller number of sites than those where it doesn't.
To eliminate the possible conflicts, I've added the plugin to a site, activated with an unmodified twentyeleven theme, and no other plugins installed, except for the Social plugin, and the issue still occurs - see: http://plus.agentevo.com/blog/decorating-a-contemporary-dining-room/
Any help/fix would be greatly appreciated. Thanks!