The browser back button is based on the browser's recollection of pages it's loaded, and doesn't understand that when you switch boards, two new pages get loaded: The new board's TOC, and its banner at the top. Basically, the browser Back button goes a half step at a time; first time switches the TOC back, hit it again, it switches the banner back.

The phenomenon Tom describes is another way the browser and UI aren't connected. Reloading doesn't necessarily take you back to Space, but that's probably what Tom's bookmarked--the URL has a suffix identifying the board, e.g. "?SvcPt=Space". Reloading reloads that URL, regardless of where you've travelled since.

My advice: Don't use the browser controls. Web user interfaces and the browser controls rarely place nice together.