Yeah, happened to me too. Whenever I refresh the screen tracking my subscribed threads, it marks everything the screen showed previously as read (even though I didn't read them).
Also, I just responded to the thread Why Defenses (saves)?, and now that thread isn't being removed from my subscribed threads list, despite that it has been read. It shows as read, but every time I refresh it's still there.
EDIT: This thread now appears on my subscribed threads list as well, despite that I'm the most recent poster (and therefore all posts have been read).