This problem has been happening for a week or two. It started around the same time I first noticed the new "show/pause live updates" buttons on the home page. I see it both with Firefox 3.6 on Linux and Safari on Snow Leopard.
Basically, there are two things wrong. They are regressions, in that they used to work previously.
First, when I return to the home page via the back button after reading a post, the list of recent threads isn't updated. It's the same as the last time I saw it, even though there has been activity in threads while I was away. I've tried pressing the "show live updates" button. It refreshes the list, but doesn't appear sticky. It's also unclear what the gray vs. white means here.
Second, the indication of how many unread posts there are for me on a given thread is no longer updating. I see this on the home page and in my profile. Enabling "live updates" doesn't fix this. I'm wasting a lot of time re-reading posts because of this.
I'm somewhat surprised I haven't seen a report on these issues already. As far as I can tell, they're rather obvious, pervasive and annoying.