this is not unique to DL. It used to happen at NW in the pre-integration days. A number of times, return flights on the same day would show up as not mileage eligible.

My solution in the past was a simple phone call to Chisholm to get it correctly posted immediately. Now it requires a call somewhere (for me SLC) to get a request generated for the miles and having them post sometime in the future.

Really not worth getting upset about. Now when they stop providing a toll free number that will be the time to go ballistic.