We are finding that many people who have their problem solved now want to ask a followup question, and the natural thing to do is reply in the same thread. I don’t want to close or lock threads automatically, because often there is actually additional useful information on the original problem. But new questions shouldn’t go in the same thread, because:
They clutter things up for people looking for solutions to the original problem
They make the new problems harder to find and search for
Now there’s a thread with multiple problems and multiple solutions, so nothing can really be marked as a solution.
The proper thing, of course, is to use the secret → + New Topic functionality, but that’s really, really not obvious. I’d love a “Followup Topic” question to appear next to “Reply” on topics with a solution — or any closed topics.