Editing notifications does not allow editing of attachments

Press "Edit" button in course element "Notification" (Mitteilungen):

1. Open a course which includes the element "Notification".
2. Create a new notification with an attachment.
3. Click on the "Edit" button.

-> OK: The text of the notification can be edited.

-> NOK: The attachment can not be edited. It actually is not visible in the edit mode.

Expected behaviour:

Clicking the "Edit" button should allow you to change the text and the attachment.