I'm not sure if this is a Forums query or general WPMU query.
I have the forums plugin network activated on my site.
On the primary site the (using default buddypress theme) it automatically has navigation for forums, groups etc. even if no forums or groups exist.
However, in a network site, the navigation only says 'Home','Sample Page', with no links to forums (and no links to groups, but not having network site groups is a whole other issue)
I have added a forum to the network site, navigation does not update.
I am aware that I can go into appearance -> menu and create a custom menu with links to the forums on the network site. However this is not scalable, to ask every site creator to set up their own menus and navigation after registering.
I'm aware that this is not strictly an issue with your plugin, and more likely and issue with the default behaviour of the theme itself.
However, has anyone yet come across this and solved it? (most likely a theme edit, which I am about to look at myself now - if I solve it I'll be back soon.. I just wanted a rant)