janice shell, I have been seeing the same result, only more drastic, on the 'next 50' choice. See my post 111900. Found a way that works until they get it fixed.
Read to the end post, either 20 or 50, and change it's digits to the next desired post number. Then hit the 'GO' button to take you to the new post as a single. Just hit 'next 20' or 'next 50' from there, and you'll be right where you want to be at the top of the new list. It has been working for me, and it is a lot easier than the other options I tried. I hope they get that, and the problem with not registering as read, cleared up soon. It is a real pain. GLTA LC