The Trollest Of Trolls
this is a function of the forum software alert system. the way its defaulted is that a new alert is given and once you "see" (click on the bell), the system feels you've seen the alert and you no longer need to be alerted. one of the frustrating things is that if you don't click on the alert and read up through the thread, it thinks you no longer need alerts for that particular thread. we're using an addon to sort of counteract that behavior.When you look at the "bell" icon in the upper right corner, it shows recent posts in threads that you are have posted in/subscribed to (although it always seems to be a bit erratic - sometimes I get 12 alerts, sometimes I'll check in after a day or two and there won't be any alerts at all).
you can click on this in the alerts list to mark the alerts as unread:Under the old format, newer alerts that I hadn't already looked at had a little yellow asterisk to indicate that they were unread.
Under the new format, that doesn't seem to happen anymore and so it's more difficult to tell if you've already looked at a post/thread or not.
if you want to alter the way alerts are presented you can go to your account page and preferences to see the settings for alerts:
checking alert page skips mark read should stop the annoying default behavior i mentioned above.