Delta used to require a manual "cleanup" of the reservation. However, they've started doing this automatically. Its still a good idea to check your reservations perhaps weekly especially if you have a "special" seat (exit row) so you can hopefully get it back. I know that many of you are on award tickets for this, if a schedule change leaves you with an uncomfortable connection time, they will reaccomodate you to an earlier flight even if "regular" award inventory isn't available. If the agent refuses to do this for you, just hang up and call back.