I just started noticing this in the last week or so. It seems posts added to a thread when I am responding show up later as if I have read them.
They weren't there when I started posting. They don't show when I just finished posting. I see them later on the thread and they are "closed" as though I have read them.
Also seems as though the site has been a little slower than usual. Other sites I frequent are working fine, so I don't think it is my service provider or computer.