Sometimes I'm an idiot and when the new posts for a given thread span a page break, I miss it and accidentally go back to the index instead of clicking on to the next page. The old software would leave the second page's posts marked as unread, but the new software marks them read. The old way is better since sometimes I only just barely notice that there's another page, which makes me wonder how often I've just skipped past a page's worth of posts because I don't realize that they're there.