I find this pretty confusing... and hereby lobby not to have the interface change in this manner, based on whether there are further generations. These kinds of tweaks to an interface based on subtle differences are not part of web design 101...
Fankly, I would lobby to put the original Family Tree tab back where it was and restore it as a full fledged page of its own... the current situation with anchors is cumbersome, including when trying to share links to the tree -- sometimes the URL doesn't update to show the #Ancestors hash arg, for instance).