Same for me

Using W2000 Pro SP4, along with IE 6.0.2800.1106

Along with the "coloring" problem, it also mean that you are directed to the very first post each time you open the thread, and no longer to the first unread post.

As for the folder icone in front of a thread , it looks like it doesn't turn white if ALL posts have not been read. Not sure ; had this on one thread.
If confirmed, that would mean it's no longer possible to mark a thread as read, just by reading one post and ignoring the others (if not interested)