Drag-drop markers: Changing the shape in IE makes it to disappear

(taken from MDL-62411, pay special attention to IE and the change-shape detail)

Note: These changes need to be tested on a range of devices, including Chrome, Firefox, IE, and Mobile devices however, most of this testing was already done during MDL-62411

Setup

1. Create a course with a student enrolled in it
2. Create a new Quiz

Creating a new question

1. Edit the quiz
2. Start creating a new drag-drop markers question
3. Complete the required fields.
4. Try add a background image. Verify that the preview updates.
5. In the Drop zones section, set a marker shape. Some coordinates should appear, and the shape should appear in the preview.
6. Edit the coordinates
   1. The preview shape should update to match.
7. In the Marker section, type a marker name.
8. That marker name should be be available to select as the marker for your drop zone. Select it.
   1. The marker name should now be shown on the preview.
9. Edit the marker name
   1. The preview should update immediately with the new name.
10. Click on the drop zone in the preview
    1. Some handles should appear
11. Drag the handles
    1. The shape should change, and the coordinates in the form should update in real time.
12. Add more markers and drop zones.
13. Change the shape of a drop zone
    1. The coordinates and the shape in the preview should change to match.
14. Change one of the shape to polygon.
15. Hold down CTRL and drag a marker
    1. This should add an extra marker to the polygon.
16. Save the question, and preview it.
17. Drag the handles into the relevant areas and save
    1. Confirm that it marked the response correctly

Editing an existing question

1. Edit an existing question test that the above manipulations work there too.
2. Try loading a different background image. Verify the form updates correctly.

Attempting questions as a student

1. Login as a student
2. Attempt the quiz containing the question
3. Try to get it wrong and right in various ways