OK, two things. Thing one: that's about the least intuitive procedure as I've seen in recent times. Thing two: it only blocks the topic from the "Unread Posts" view; the topic still appears everywhere else. That's about as useless (for me) as I could imagine, since I normally don't use the "Unread Posts" view because that's more difficult to navigate and make sense of than the plain old top-down view. Oh well, hope it helps other folks.