This has been happening since I first ever registered on the forums a couple years ago, and I am annoyed it still hasn't gone away. In any browser I use, on any computer, as long as I don't close out all browser windows, my read topics stay remembered. However if I close all browser windows, when I come to the forum again it marks an arbitrary number of recent topics as unread and I have to click the NEW icon on each of the ones I had already read. Strangely though I don't have to log in again ever.
This is pretty annoying and the fact that it happens to me on all of my computers with all browsers confuses me. Surely someone else must be having this issue?