A cross-reference to an endnote in OOo Writer can be used to refer to that
endnote more than once without incrementing the reference number. 
Unfortunately, the cross-reference is deleted if the original reference in the
main text is moved.

In other words, if the original reference in the text is contained within a
highlighted selection that is drag-moved with the mouse, or moved by cut/paste,
then the cross-reference is lost.

This is a defect because the endnote being referenced has not been deleted.

To replicate this problem, first type in some text and insert an endnote.  Type
in some more text and insert a cross-reference : INSERT -> Cross-reference...
and select Type=Endnotes, Format=Reference.  There should now be an original
reference in the text, and a cross-reference in the text.  Now highlight
(select) some of the text which contains the original reference, and drag-move
it with the mouse.  After this, you should notice that the cross-reference you
inserted is no longer there.