My friend was in Map Editor and I invited him to join my tribe house. He clicked [join] and then he was in the tribe house but still on map editor. He could also see the tribe house chat as well.

I've seen thing's like this during the Valentines event.My friend's are offline but my list say's there online.But it's fixed now.It should be fixed soon ;)
Or probably you left you're friendlist opened up and it was you're lag
That's either one of question's..