When I click 'view new posts' I get a few pages of new posts.

It used to be that as I went through each page the posts were marked as read.

Now I have to click 'mark all posts as read and return to ????' to get them marked as read, otherwise next time I do 'view new posts' I get the same posts listed again.

Have I changed something or has TV changed?

There has been a problem with the system software with that issue and a recent update should have corrected it. But have seen some reports of that not being the case. Be sure to clear your cache, log out then log back in and see if it improves. Probably a cookie clear may be a good idea also.