St. Tim -- could this be cookie related?
Hmmm... it may be indirectly cookie related. Without more info its hard to be definitive, but here's idle speculation... and its long.
Assume Dennis' description of how he navigates is typical for showing the 'problem'. I see it too if I follow the navigation he described.
The UBB software needs some way to track which threads have been read by an individual. A couple ways this might happen are
1. keep this information in the user's current session on the server. (a 'session' is a bit of memory where the server keeps track of things related to a specific person, for example what options s/he has chosen, during the time they are considered 'logged-in'.)
2. keep this information in a cookie.
Either method is a way for information to persist from one page to the next. Web pages have no inherent connection to one another so some means external to the page is used to share information across pages. A session or a cookie is a means to persist information from one page to the next.
Still with me?
In order for the forum software's information to get updated based on a user's activities (EG reading a previously unread thread) the information must be sent from the browser to the server. The server will then update the data in the person's session, or it will send an updated cookie. In either case, this require a request be made from the browser to server in order for the info to passed to the server.
Using the Back Button to navigate does not typically cause a server request to be made. Usually the back button takes the previous page from the browser's cache. This is much faster than a round trip to the server, but it only can show the page in the state it was in when it was first visited. It will not reflect changes between the time the user left it and it is drawn from cache. Thus - using the back button doesn't tell the server that a thread was read - w/out this info it can't update either cookie or session. So when one returns to the forum list via the back button, even from the main page if was backed-in-to, the same threads show as unread.
However, based on some experiments, I think the server updates are occuring based on a person logging-in. A simple way to check this is to open a new browser window - not a clone of an existing window (don't do Ctrl-N - open with the desktop icon). The new browser window should show the forums correctly reflecting the latest state of a user's activities including those from the other browser. Each concurrent login would have its own cookie, so the info is probably being kept on the server side.
Bottom line -
a. if you want to the forum software to do its job, don't use the back button to navigate, click links based on where you want to go.
b. each time you want to access the forums, start a new browser.
These things may reduce the problem. Ultimately it sounds like the UBB code needs to do a little better job tracking the current state of each user. The software does do this for some things but not everything. For example, the fact that a person has replyed to a message is always shown on the main page if you use forum navigation and not the back button. The authors may have chosen not to do update everying with each click or each new page because it adds a lot of extra overhead and slows things down.
Or, it could be something totally unrelated. :-)
Honk if you made it this far.
T