New Posts Icon not showing up sometimes

Ill try to explain this as best as i can and see if anyone can help me. You know the icon that changes when someone posts a new topic or new reply, well sometimes it doesnt change so I dont know if theres been a new post.Also, sometimes I will see it change but not go into the forums just yet to read and may go to another site or close my browser and when I go back to my forums it no longer shows a new post icon.Its as if it knows i saw it but i never clicked on it to read it so why does it keep reverting back to no new post icon.Its very hard to tell if i have new posts and frankly its driving me crazy.

It's been happening at my forum too. It is really annoying and has been happening more often to me; sometimes all I have to do is read a post on my forum and when I go back to the index page, all the new posts icons are gone. Others have also complained of this happening, both here about this happening at other forums and to me from members of my forum.