I would like a moderator to respond to this so I know it has been noted as a problem, otherwise I will start pesky PM's
When using PM's It seems unusually hard to navigate back to the forums. Perhaps moderators have a different page for PM's and do not have this difficulty. If so create an account and go into the private message areas and try to navigate back. I recently went to site map at bottom of screen and then clicked sciforums.com. It should be easier.
I'm having trouble understanding your problem. When I want to PM I click on the persons ID and select PM which takes you to an advanced PM window. When done if you click your back button a time or two and your right back where you started, or you can select the Forum tab to the sub-forum listing. I haven't found a forum that's any easier than that.