When I save a copy of my LibreOffice odt document in Microsoft Word, some of the internal hyperlinks are corrupted (including in the original document). When I bring the Word document into Calibre to create an epub, these corrupted links are included in the NCX, even though the bookmarks they target are preceded by ref_ .
If I correct them in the original document and save another copy to Word, the same or other links are corrupted and again included in the NCX. The selection of which links are corrupted seems random.
External links are fine.