Why won't 5.1.4 read my .doc (Word 97-2003) bookmarks?

My company currently uses the openoffice java API to access OpenOffice running in headless mode to read a .doc file with bookmarks, replace the values of those bookmarks, and generate a pdf. We are looking to upgrade to LibreOffice. In testing the code, I discovered that the LibreOffice executable does not seem to be able to see most of the bookmarks in the document. This is also apparent when I view the document in the Writer gui. The OpenOffice gui displays the bookmarks in the navigator, while the LibreOffice navigator does not. The problem goes away if I save the .doc file as a .docx. Because of the number of .doc files involved, updating all of them to .docx is not really an option. I’m hoping someone else has encountered this problem and can provide some assistance.