Navigation topic is just a static page that typically serves as a "parent" to other pages. I've noticed that this typically happens if I edit either that particular parent page or any of the "child" pages. And, it doesn't always occur every time. Just some times.
Not every time?...hmmm then it's very strange. I tested it, but can't recreate it. Created 2 pages, one parent and one child, added them both to the navigation, and edited them both several times, but nothing happens.
I've been using BF for two years and never had this issue til we upgraded to WP 3.4
You might need to upgrade the theme too. The latest version 22.214.171.124 is a Wordpress 3.4 compatibility release.
btw, I recommend to enable the "Cache the settings stylesheet" setting. It writes the theme setting styles to a file and speeds up the website. More info.