The forum issue where it randomly decides to mark everything as having been read, still exists. I remember reporting this problem eons ago too :/ (Other forums like PureZC don't suffer this issue).
Forum Issue : Intermittently marks everything as read
I have noticed this happening too, but only if I hang around on one page and don't come back to AGN for a while, then it seems to reset my viewing. Not sure if there is some kind of idle counter or something that resets this or not.