Impossible to set "Locked" when creating the grade category (only when editing)

When creating a gradebook category with multiple items, the category title for that category and any items in the category cannot be locked.

To Reproduce:
1. Create a course
2. Create a category "Quizzes" in the gradebook
3. Create two grade items "Q1" and "Q2" in the category
4. Edit the category's settings and click the 'locked' checkbox under Category Total
5. Save changes and return to Categories and Items
6. Edit the category's settings again and see that the 'locked' box is not checked

For a category with two or more items, the 'locked' box will not stay checked after saving changes. Items in the category also remain unlocked.

7. Delete one of the items in the category
8. Edit the category's settings and lock the category total
9. Save changes and return to Categories and Items
10. Edit the category's settings again and see that the 'locked' box IS checked.

If the category only contains one item, the category totals will lock properly.