My feed list includes read items even if it’s set to unread only.
It happens consistently with some feeds (for example, Boing Boing, attached). It’s frustrating because if I view an entire folder, they appear there and sort of break the whole reading experience.
On some feeds I did some dance of insta-fetching stories, marking all as read, deleting the feed, re-adding the feed and they started not doing this (I think an example that worked on for me is TechCrunch). But some this hasn’t helped on.