Changing 'Students submit in groups' from Yes to No on activity with submissions removes existing submissions.

Steps to Reproduce:
As Teacher:
1) Create Activity of type Assign.
2) Select 'Students submit in groups' to Yes.
3) Leave selection of 'None' for 'Grouping for student groups'
4) Save Activity.

As Student:
1) Submit file to activity.

As Teacher.
1) Access grading page, select 'grade' for student and verify file is present.
2) Edit activity
3) Set 'Students submit in groups' to 'No'.
4) Save activity.
5) Access grading page, select 'grade' for student and verify file is now missing.
6) Select 'Download All Submissions' and error 'Nothing has been submitted for this assignment' is presented.

As Student:
1) Submitted file is now missing from student view.
2) Re-submissions at this point work OK as individual, also visible as Staff.

Re-selecting 'Yes' after 'No' has been selected does not re-link assessments.

What was expected:
Remapping existing submissions to individual who submitted rather than their group.

What actually happened:
Unlinked/Lost existing submissions, but still showed a submission was received but it was not accessible.

Suggestions:
Warning on change of Group selection after activity has been created, or
Lock group submission selection once activity has been created (with message why if submissions exist), or
Remap file so it is not lost when group submission setting is changed.