Not Len but I can tell you what works for me and what I've found.
Sometimes when you go to another page you may view an external link or something similar. If you were to watch your forward and back buttons, you'll notice your back button becoming non functional for, what seems like, no good reason.
This is one of the many reasons I use Firefox although IE has tabbed browsing also. I generally start on "Todays Posts" when I come on line. I keep this open and if I want to read a thread I open it in a new tab. Then when I'm done it's quick and easy to close the tab and the original "Todays Posts" is still open in the original tab. No waiting for the page to close and another page to open back up because it's already open and sitting there waiting for you to come back.
Just a thought and I know tabbed browing isn't for everyone but with use it sure makes life easier, at least for me. Also, I make a habbit of deleting my cache and all cookies that aren't allowed and saved after each online session. Cache and cookies can cause problems also.
I will say that I don't notice the problem you talk about on LRH but with tabbed browsing I don't think I would. I will also say that even with tabbed browsing I've notice that the ability to "go back" on some sites goes away at times and I never really give it much thought as normally it's not an issue.
With the PM thing, all of my PMs get opened in a new window and that leaves the original open and waiting just like the tabbed browsing.
Maybe Len will have some better technical infor for you as far as the LRH site goes and your problem. Hope you get it figured out.