Ha, I talked with the devs just about that shortly ago.
The reason: Your file is fine. This message is not helpful, because just by opening it temporary data will be produced – and promptly deleted by the repair command. So you actually can never have a "good" file...
It's totally bonkers.
Lucas Becker | AC 27 on Mac | Editor at SelfGDL | Developer of the GDL plugin for Sublime Text | «Furthermore, I consider that Carth... yearly releases must be destroyed»