Your batch may have restored itself because not all of the shipments in the batch were created at one time therefore leaving the remaining shipment(s) open.
Anytime you list a batch using the private workflow, we must refresh the batch status as Amazon requires due to the warehouse rotation that occurs every 24-48 hours. When this happens, new shipments for the entire back can/will get created.
To avoid this in the future, there are a few options on what you can do when you don't want to send one of the shipments right away. In our User's Guide article around Creating a New Shipment, those options are available to review in detail. :)