[DiapDealer]

That's a known frustrating bug when creating mobi's with kindlegen (or at least it was at one point), but I've never come across it when converting with calibre, myself. Maybe it's actually a Kindle rendering bug rather than something to do with the mobi creation software. Does the final navpoint function normally when viewing with the KindlePreviewer app?

The solution with kindlegen was to add an extra dummy navPoint at the end of the ncx file. Just leave the text empty (nothing between the <text></text> tags in the navLabel) and make sure the src attribute in the <content /> tag is valid.

That made sure the next to last (the real last) worked fine and the dummy navPoint was ignored in the final mobi.

But like I said, that was with kindlegen and not calibre, so I don't know if I've been any help.