[Despite best efforts, c]harts with regional maps contain extensive geographical information that LibreOffice is unable to preserve.

Were I the devs, I'd be opening those files read-only by default and having an "unlock to edit" option somewhere obvious. When clicked, it would pop up a dialog box with the yellow triangle / exclamation mark warning icon saying that things would not be preserved beyond that point.

LibreOffice already does something like this when saving in formats that can lose information, but I'd move that to right up front.

I might even include a dig that the document was created by software that does not follow open document standards.