I am 99.9% sure that the little gray and red "New" flag on unread threads has changed its M.O. for the worse. Here's what happens: I go to my CH profile page and see a bunch of New flags on threads which have had additional posts since I last read them. I click on one of these threads, read the new stuff, then hit the back arrow adjacent to my browser, which brings me back to my profile page. The thread I just read still has the New flag. Didn't that used to disappear? Now, it only disappears if instead of the arrow I click on my user name at the top right corner of the page.
Same thing when I read a thread to which I have not posted. If I hit the back arrow to get back to the list of threads on the board, the New flag remains. If instead I hit the name of the board, in the bold caps above the threads list, the New flag is gone.
It's not a huge deal, but it is easier and less confusing to click the back arrow rather than scrolling up to the top of the page to hit the board name or my user name.