Warning: non-technical person talking

I know that the lightbulbs indicating new posts are based on cookie technology. And normally they work fine for me. But 100% of the time, if I click on a hyperlink within a thread, read it, close the new browser window, and then hit back on the original window, all the lightbulbs are reset. If I don't open the hyperlink and hit back, the lightbulbs that were there when I opened it still exist.

Can anyone 'splain that to me??