Imported/Restored assignments have no submission/feedback plugins enabled/settings lost

If you take a assignment and import (or restore it) in into a new course, students cannot submit to it. After more research, mdl_assign_plugin_config is not populated, meaning no submission/feedback plugins are enabled, and will reset to defaults once the assign is edited and saved.

To reproduce:
You need two courses (A and B), B needs to have at least one student.

1. In course A, create an assignment with default settings.
2. In course B, select import. Find course A and import only the create assignment.
3. Become one of the students in course B and enter the assignment. You will see "This assignment does not require you to submit anything online"
4. Become an admin or teach in B again.
5. Edit the imported assignment, make no changes, but go down to the bottom and click Save.
6. Become one of the students in course B and enter the assignment. You will be able to submit.

Note that the settings are not preserved at all, all of the lost settings are reset to their defaults, regardless of what was set.