Today after you 'Send' a scheduled message, the message shows up immediately in the "Sent" folder. But actually, the message hasn't been sent. To confirm that it hasn't been sent, you have to go into PM > Campaigns > Scheduled sends to verify the message is still pending. It would better if the scheduled message sits in the Outbox folder while it's pending, and it goes to the "Sent" folder only after it has been really sent.
Internally submitted idea.