When in split view, when using the Mark Everything As Red option, it does update all of the unread counts and if I leave the folder and return, it reflects it properly, but the story titles themselves are not updated to reflect this. So the list of stories still looks like there are unread but the pane on the left disagrees.
It handles it on folders and feeds, but not when using the Mark All as Read dialog. That’s a bug I’d like to fix.
A workaround might be to include that Mark As Read checkbox that is available when opening a specific folder to All Site Stories. Thought I doubt that would be any easier