Thanks for the explanation . I can understand the reasoning but I have to agree with Chosker in that there would be better approaches.
Ideally a question would only become reopened explicitly (this could be an option when posting a comment on a resolved question). That way people could still add closing comments, or could come to an old question and add updated info or another solution, without the question being changed back to ‘unresolved’.
The staff post auto-resolved thing is not really a major issue, but people will generally expect that it is up to them to decide if/when their question is resolved to their satisfaction. I think it can give the wrong impression and turn people away from the system. Perhaps an alternative would be to put something in place to encourage people to remember to mark posts as resolved, such as a low limit on the number of open questions a user is able to have at any one time.