There were some issues with the new 'Unread Topic' highlighting where a forum icon was still showing unread, even though all topics had been read. See the previous post for details.I have changed the forum settings to correct this, but you will now find numerous forums highlighted, even if you have read the posts.
Once you have established that you have read everything, click "Mark forums read" on the forum home page. The unread highlight should work correctly from then.
The unread post highlighting for Guests or members who haven't logged in will remain the same. The problem may be an issue with individual internet browsers, so until a bug fix can be found, if you find that the forum icon is still highlighted as unread after you have read everything in that forum, then you will still have to manually clear it using the "Mark topics read" in each forum section, or "Mark forums read" on the forum home page.