Description:
When saving document to DOCX, bibliography links are broken and cannot be restored. They are lost.

Steps to Reproduce:
1. Create a new LO Writer document
2. Insert some Lorem Ipsum paragraphs
3. Create a few new bibliography entries with the source being Document content and insert them into the document.
4. Create a Bibliography Index at the end. The index should be populated fine. Edit the index and change the entries to 'Number entries' instead of short name display.
5. Save the document as DOCX and close LO Writer.
6. Open the document again. Notice that the bibliography references are missing the [ ] brackets.
7. Update the bibliography index.
8. Notice that all links are now broken: !!br0ken!!
4. 

Actual Results:
The bibliography index is now broken. All indexes are lost and the references are no longer in the document content. You must insert them manually again.
All the indexes in the Bibliography index show !!br0ken!!

Expected Results:
The bibliography index should remain the same. Nothing should be lost. The [ ] parantheses should remain in place.


Reproducible: Always


User Profile Reset: No



Additional Info:
This reproduces every time and seems to reproduce regardless number entries is checked or not. So short name entries will be affected too.