Discourse has a slightly different notion of “pinned” (sticky) than the previous forums. In Discourse, users will not see pinned topics they have read at the top of the list anymore. SMF and others always list pinned/sticky topics at the top, whether they have been read or not.
So, I want to vote for the old behavior. It’s controllable by a switch in the admin settings–one checkbox apparently makes pinned posts stay at the top of lists whether they’ve been read or not.