Conversion from mobi (to mobi, or epub) breaks internal links
 

I've a mobi file, generated from Word via HTML with the Amazon downloadable.

I need to convert to epub, as well as use the conversion in Calibre to add a proper TOC and embedded cover. That is all going well. But Internal links added in Word, and that work fine in the HMTL and original mobi version are broken in anything that Calibre has worked on.

Looking at the epub in Sigil suggests that all links are being converted to

Any pointers would be very welcome.

Issue persists, but using HTML as basis in Calibre seems to do a better job.