The number in the blue/grey bubble is the number of responses to that thread at the time the thread listing was retrieved by the app from the server. If you stay within a forum for a period of time then this number can go stale, as other responses may be generated whilst you are reading the thread. The thread listing is not refreshed unless you exit the forum, pull down to refresh the threads or in certain circumstances make a change to a thread. The forums list is refreshed in the background periodically(this can be disabled in settings) or every time the app comes to the foreground if you have switched away from the app.
The delta time.
These two items are meant for guidance. But I see how leaving the device and coming back to a stale listing can result in something that can be counter intuitive. Updating the delta displayed on the device is one way of easing the problem. It is non trivial though. Will think about this one.
Thanks for taking the time to offer you thoughts. It is much appreciated.