Content reduced to the edited section in section editing with a display sheet

Steps to Reproduce:

1. Disable inplace editing by setting edit.document.inPlaceEditing.enabled = false in xwiki.properties (not necessary, but makes it easier to reproduce)
2. Create a new AWM application with a title, content and a short text field.
3. Create a new entry in the application and add several sections of level 2 in the content.
4. Click on the "Edit" button in the content menu
5. Append ?section=2 to the URL
6. Click "Save & View"

Expected result

The document is unchanged.

Actual result

All content but the second section is lost. The text " (§2: Second Section)", where "Second Section" is the second heading, has been appended to the title.

I haven't found a way to easily reproduce this while just clicking buttons in the UI but this can be easily reproduced on https://design.xwiki.org/ where section edit links are displayed in the content of each proposal which lead to the exactly same edit screen as in the reproduction steps with the exactly same bug (this is how I found this bug). This means it is definitely also reproducible on 13.10.3 but the bug is probably much older.