Description of problem:
The link path from an xlsx sheet to external data of another xlsx document gets always doubled after closing and reopening the xlsx document, even after having it saved correctly.

This problem does not exist in Windows version and in version 5.3.7 in Linux from the distro repos.

How reproducible:
Always

Steps to Reproduce:
1. Create a calc sheet with LibreOffice 6.1.5 with a link in it to some data of another calc sheet and save them both in xlsx.
2. The link to the external data in the first xlsx sheet is correct and everything works fine.
3. Close the xlsx document and reopen it, then the path to the external data ist doubled.

Actual Results:
The external link after closing and reopening the document:
file:///home/name/documents/home/name/documents/datadocument.xlsx

Expected Results:
The external link before closing the document when everything is fine:
file:///home/name/documents/datadocument.xlsx

Additional Info:
The calc sheet should keep the link like saved and not change it after closing the document.
This bug seems to be valid for all 6.x.x versions (i didn't try 6.2.0)

I also posted a bug report on bugs.documentfoundation.org, bug nr.:
https://bugs.documentfoundation.org/show_bug.cgi?id=122015

This bug makes Libreoffice unusable in an enterprise or corporate environment, because there is no way to save the calc sheet so other poeple can open it without problems.