Can't reorder XClass properties with the class editor

Steps to reproduce, as an advanced user:

1. Create a new `Sandbox.Test` page.
2. Save the new page with an empty content.
3. Open the "Edit" dropdown and click "Class" to open the class editor.
4. In the new property line, fill in and submit the following properties:
   1. Name: "testA", Type: "Number"
   2. Name: "testB", Type: "Number"
   3. Name: "testC", Type: "Number"
5. Click "Save and View".
6. Open the class editor again through the "Edit" dropdown.
7. Drag the "testC" property between "testA" and "testB".
8. Make sure the order is "testA", "testC", "testB".
9. Click "Save and View".
10. Open the class editor again through the "Edit" dropdown.

Expected Result:
 The class properties are listed in the new order: "testA", "testC", "testB".

Actual Result:
 The class properties are listed in the original order: "testA", "testB", "testC".