Endnotes opening as footnotes on certain Kindles from .mobi file. Urgent help needed.

Hi all

I'll try and keep this brief, but I need to fix this fairly urgently as it's affecting a 'live' book.

Working on a non-fiction book for a client recently, I generated the original book with footnotes in InDesign, exported it as an ePub 3.0 with footnotes.

Then, in Sigil, I moved all the footnotes - which were collected in sections at the end of each chapter - to a new Endnotes section at the very end of the document.

I tested that. Saved that ePub. Opened and tested that in Kindle Previewer and - as hoped - the endnotes worked appropriately: ie: click on in-body reference number and you get whisked to end of publication. Clicking on the linked reference number in that endnote section takes the reader back to the point of origin in the the book.

Anyhoo, today, the client has informed me that the 'live' distributed version of the book is displaying the endnotes as footnotes on his and at least one other Kindle.

To be specific: click on a note reference and the Kindle pop-up window is activated. If your were to click on the 'Go to Footnotes' option in that pop-up, it would take you to the Endnotes section and you could do the round-trip. BUT, this was not the agreement I'd made with the client.

Bottom line: what do I need to do to the file to switch off the pop-up functionality and guarantee that only the endnote option is enabled?

Oddly, if you test the same distributed file in any Kindle viewers such as the following:

• Kindle Reader for Mac
• Kindle Reader iPad
• Kindle Reader iPhone
• Kindle Cloud Reader
• Kindle Previewer.

the endnote function works straight away!

Any help / guidance would be very much appreciated as I want to put this job to bed.

Thanks in advance!

M