If you're using the manager, there's probably a bug.  I'll have a look and try to get it taken care of in the next couple of days.  I should note that we're starting to move things away from the site manager and more towards inline editing.  For example, if you go to your site, which should be a Community (i.e. Index page), you'll be able to edit forum names and their position in the Community directly.

There's another way to edit your site name and tag line.  You can use the Starter Designer to change it - you need to click on the cog menu in the upper right of the page.  It's next to the login menu when you're logged in as an admin.  Choose the Starter Designer option, and then click on the Title and Tagline tab to edit your title (clicking on the Continue button will save your changes).

Anyway, give that a try and let us know if that works.  In the meantime, I'll take a look and see what the bug is in the Site Manager.