- Open the OpenOffice Writer or a new Writer document
- check that "Tools" > "Options..." > "Load/Store" > "General" > "Save URLs
relative to" options are both not set
- insert a Hyperlink (Insert > Hyperlink from the menu bar or Hyperlink from the
Toolbar)
- chose type document and enter a relative path starting with the current
directory (like ./file.txt)
- Apply and Close the hyperlink dialogue
- open the Navigator, open the hyperlink just created and check the document
path: it should still be as entered
- Save and close the document
- reopen the document
- open the Navigator and check for hyperlinks: the hyperlink is gone!

The "content.xml" in the document.odt file contains a line that reads:

<text:a xlink:type="simple" xlink:href="">./file.txt</text:a> 

If the document is saved as HTML the link looks OK:

<P STYLE="margin-bottom: 0cm"><A HREF="./file.txt">./file.txt</A></P>

The problem does not occur if the “Save URLs relative†options are set.
Apparently it is the “Save URLs relative to file system†option that matters.
Apparently it doesn't matter if the file targeted actually exist or not.