In my preferences I have set a few categories to be muted – one of them is Dorico. I am still getting Dorico posts in the “new posts”, and when I return to my preferences, I find the Dorico category is not muted.
I think I assumed that muted categories would not appear in the New or Unread lists. Even if this is not true, I have added Dorico to the muted categories several times, and it never stays there.