Boost For Lemmy

I have the preferences set to not show read posts, but still see posts in my feed (shown grayed out) that have been hidden. I think they are posts from another instance that is federated (like maybe I hid them on the other instance). Is hide (the checkmark) not the same as mark as read? And, even if not, shouldn't a hidden post stay hidden? If it is greyed out, the app knows it has been seen (or marked).