Hopefully you can replicate this as an issue to be able to squish another little bug....

I've got a closed group and use the invite feature to send an invite to a friend. They click to the 'Accept Invitation' link in the email they receive... they're not logged in so the first thing they get is the login screen... once through that they see the attached screenshot...

It's the right group... but it looks like an empty message in the green bar at the top... and no auto-join... the button still says "Join this Group" and they have to click that (and then they're in fine)... so the main problem seems to be that blank green message bar.... should it tell them to click the join button... or should it (ideally) be confirming that they have joined the group and nothing further is needed?