Sorry for originally putting this question in the wrong place. I wasn't sure if you wanted this level of detail in the plugin thread.
The odd thing with the duplicate keys is that according to Calibre, those two elements don't point to the same thing:
Part I - Things Slow Down points to OEBPS/part-001.xhtml#toc_2, while Chapter 1 points to OEBPS/part-001-chapter-001.xhtml
Editing the book in Calibre and looking under the Miscellaneous area at toc.nxc, there's the following:
Code:
<ncx xmlns="http://www.daisy.org/z3986/2005/ncx/" version="2005-1" xml:lang="en">
<head>
<meta name="dtb:uid" content="urn:uuid:01019BD2-D0FE-48A4-AB7F-4186CCC1181A"/>
<meta name="dtb:depth" content="3"/>
<meta name="dtb:generator" content="calibre (5.34.0)"/>
<meta name="dtb:totalPageCount" content="0"/>
<meta name="dtb:maxPageNumber" content="0"/>
</head>
<docTitle>
<text>Immortal and the Island of Impossible Things</text>
</docTitle>
<navMap>
<navPoint id="num_1" playOrder="1">
<navLabel>
<text>Cover</text>
</navLabel>
<content src="OEBPS/titlepage.xhtml"/>
</navPoint>
<navPoint id="num_3" playOrder="2">
<navLabel>
<text>Part I - Things Slow Down</text>
</navLabel>
<content src="OEBPS/part-001.xhtml#toc_2"/>
<navPoint id="num_4" playOrder="3">
<navLabel>
<text>Chapter 1</text>
</navLabel>
<content src="OEBPS/part-001-chapter-001.xhtml"/>
</navPoint>
<navPoint id="num_5" playOrder="4">
<navLabel>
<text>Chapter 2</text>
</navLabel>
<content src="OEBPS/part-001-chapter-002.xhtml"/>
</navPoint>
<navPoint id="num_6" playOrder="5">
<navLabel>
<text>Chapter 3</text>
</navLabel>
<content src="OEBPS/part-001-chapter-003.xhtml"/>
</navPoint>
<navPoint id="num_7" playOrder="6">
<navLabel>
<text>Chapter 4</text>
</navLabel>
<content src="OEBPS/part-001-chapter-004.xhtml"/>
</navPoint>
<navPoint id="num_8" playOrder="7">
<navLabel>
<text>Chapter 5</text>
</navLabel>
<content src="OEBPS/part-001-chapter-005.xhtml"/>
</navPoint>
<navPoint id="num_9" playOrder="8">
<navLabel>
<text>Chapter 6</text>
</navLabel>
<content src="OEBPS/part-001-chapter-006.xhtml"/>
</navPoint>
</navPoint>
<navPoint id="num_10" playOrder="9">
<navLabel>
<text>Part II - There and Back Again</text>
</navLabel>
<content src="OEBPS/part-002.xhtml#toc_2"/>
<navPoint id="num_11" playOrder="10">
<navLabel>
<text>Chapter 7</text>
</navLabel>
<content src="OEBPS/part-002-chapter-007.xhtml"/>
</navPoint>
<navPoint id="num_12" playOrder="11">
<navLabel>
<text>Chapter 8</text>
</navLabel>
<content src="OEBPS/part-002-chapter-008.xhtml"/>
</navPoint>
<navPoint id="num_13" playOrder="12">
<navLabel>
<text>Chapter 9</text>
</navLabel>
<content src="OEBPS/part-002-chapter-009.xhtml"/>
</navPoint>
<navPoint id="num_14" playOrder="13">
<navLabel>
<text>Chapter 10</text>
</navLabel>
<content src="OEBPS/part-002-chapter-010.xhtml"/>
</navPoint>
<navPoint id="num_15" playOrder="14">
<navLabel>
<text>Chapter 11</text>
</navLabel>
<content src="OEBPS/part-002-chapter-011.xhtml"/>
</navPoint>
<navPoint id="num_16" playOrder="15">
<navLabel>
<text>Chapter 12</text>
</navLabel>
<content src="OEBPS/part-002-chapter-012.xhtml"/>
</navPoint>
<navPoint id="num_17" playOrder="16">
<navLabel>
<text>Chapter 13</text>
</navLabel>
<content src="OEBPS/part-002-chapter-013.xhtml"/>
</navPoint>
</navPoint>
<navPoint id="num_18" playOrder="17">
<navLabel>
<text>Part III - The Priestess</text>
</navLabel>
<content src="OEBPS/part-003.xhtml#toc_2"/>
<navPoint id="num_19" playOrder="18">
<navLabel>
<text>Chapter 14</text>
</navLabel>
<content src="OEBPS/part-003-chapter-014.xhtml"/>
</navPoint>
<navPoint id="num_20" playOrder="19">
<navLabel>
<text>Chapter 15</text>
</navLabel>
<content src="OEBPS/part-003-chapter-015.xhtml"/>
</navPoint>
<navPoint id="num_21" playOrder="20">
<navLabel>
<text>Chapter 16</text>
</navLabel>
<content src="OEBPS/part-003-chapter-016.xhtml"/>
</navPoint>
<navPoint id="num_22" playOrder="21">
<navLabel>
<text>Chapter 17</text>
</navLabel>
<content src="OEBPS/part-003-chapter-017.xhtml"/>
</navPoint>
<navPoint id="num_23" playOrder="22">
<navLabel>
<text>Chapter 18</text>
</navLabel>
<content src="OEBPS/part-003-chapter-018.xhtml"/>
</navPoint>
</navPoint>
</navMap>
</ncx>
and toc.xhtml contains the following:
Code:
<?xml version='1.0' encoding='utf-8'?>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en" epub:prefix="z3998: http://www.daisy.org/z3998/2012/vocab/structure/" lang="en">
<head>
<title>Table of Contents</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
</head>
<body>
<nav epub:type="toc">
<ol>
<li><a href="titlepage.xhtml">Cover</a></li>
<li><a href="jacket.xhtml">Review</a></li>
<li>
<a href="part-001.xhtml#toc_2">Part I - Things Slow Down</a>
<ol>
<li><a href="part-001-chapter-001.xhtml">Chapter 1</a></li>
<li><a href="part-001-chapter-002.xhtml">Chapter 2</a></li>
<li><a href="part-001-chapter-003.xhtml">Chapter 3</a></li>
<li><a href="part-001-chapter-004.xhtml">Chapter 4</a></li>
<li><a href="part-001-chapter-005.xhtml">Chapter 5</a></li>
<li><a href="part-001-chapter-006.xhtml">Chapter 6</a></li>
</ol>
</li>
<li>
<a href="part-002.xhtml#toc_2">Part II - There and Back Again</a>
<ol>
<li><a href="part-002-chapter-007.xhtml">Chapter 7</a></li>
<li><a href="part-002-chapter-008.xhtml">Chapter 8</a></li>
<li><a href="part-002-chapter-009.xhtml">Chapter 9</a></li>
<li><a href="part-002-chapter-010.xhtml">Chapter 10</a></li>
<li><a href="part-002-chapter-011.xhtml">Chapter 11</a></li>
<li><a href="part-002-chapter-012.xhtml">Chapter 12</a></li>
<li><a href="part-002-chapter-013.xhtml">Chapter 13</a></li>
</ol>
</li>
<li>
<a href="part-003.xhtml#toc_2">Part III - The Priestess</a>
<ol>
<li><a href="part-003-chapter-014.xhtml">Chapter 14</a></li>
<li><a href="part-003-chapter-015.xhtml">Chapter 15</a></li>
<li><a href="part-003-chapter-016.xhtml">Chapter 16</a></li>
<li><a href="part-003-chapter-017.xhtml">Chapter 17</a></li>
<li><a href="part-003-chapter-018.xhtml">Chapter 18</a></li>
</ol>
</li>
</ol>
</nav>
<nav epub:type="landmarks">
<ol>
<li><a href="cover.xhtml" epub:type="cover">Cover</a></li>
<li><a href="title-page.xhtml" epub:type="titlepage">Title Page</a></li>
<li><a href="copyright.xhtml" epub:type="copyright-page">Copyright</a></li>
<li><a href="epigraph.xhtml" epub:type="epigraph">Epigraph</a></li>
<li><a href="contents.xhtml" epub:type="toc">Contents</a></li>
<li><a href="part-001.xhtml" epub:type="bodymatter">Beginning</a></li>
<li><a href="part-003-about-the-author.xhtml" epub:type="z3998:biographical-note">About the Author</a></li>
<li><a href="part-003-also-by-gene-doucette.xhtml" epub:type="z3998:published-works">Also by Gene Doucette</a></li>
</ol>
</nav>
</body>
</html>
Unfortunately, the book isn't free. So, getting you a copy is a bit of a problem. The version I'm working on is a download from Google Play Books that I've added to Calibre.
The following image shows the text sidebar and looks like it contains all the appropriate file names. The one thing that bothers me is that the File Preview sidebar shows a clump of things at the bottom from the toc.xhtml that aren't in the toc.ncx. I wonder if those might be the cause of the duplicates.
EDIT: that last image is pretty blurry at the forum's maximum allowed resolution. Here are a couple of the regions separately (and hopefully more clear):
and
