I just came across this myself - there seem to be a handful of things to keep in mind with whispers, and this is one of them. I was hoping to be able to use solved whispers as a part of my use of discourse as a ticket system. Often I want to mark tickets (discourse messages or topics with ticket tags) complete without informing the person the ticket is about…
[Accepted answer plugin] Add an ability to accept the initial (topmost) post as a solution could work for this but does not now.
An alternative to this seems to be making it possible to indicate whispers as the solution without exposing the whisper to non-staff. Maybe this is even a better solution in any case because then it forces us to actually write a note to explain the outcome. 