Well, there seems to be a different understanding of the term "lock". In my usage, a lock restricts the answering possibility to one special person. When I unlock, it is open to the same group of people as before the lock (Rookies, Rookies and Experts, puzzlers with less than 400 points, all puzzlers). When I lift the sub-400 limit, I definitely say so, e.g. "Open for all now". An unlocking on the Expert board wouldn't open the puzzle to pros either.