If an assign has a restriction condition that a user doesn't yet meet, and you enter an override for that user, you get the inaccurate message "Student does not have the correct group or role to attempt the assignment" and the override cannot be modified or copied, only deleted.

To reproduce:

1. Create a activity or resource with activity completion enabled, and set to 'manually mark'
2. Create an assign with a due date, and restricted access based on the completion status of the item made in step one.
3. Create a user override for a student in the course
4. Notice the warning and 'disabled' override after you save
5. In a separate browser, login as that student
6. Click the checkbox to 'complete' the activity the assign is dependent on
7. Back as the teacher, reload the overrides list - notice the override is no longer disabled, and can be edited.
8. If you toggle the activity back off as the student, you will notice the override again becomes disabled for the teacher.