Missing navigational links with XHTML chunking

I have a simple XML document:

<article>
  <sect1>
    <title>Section One</title>
    <para>First paragraph.</para>
    <para>Second paragraph.</para>
    <para>Third paragraph.</para>
  </sect1>
  <sect1>
    <title>Section Two</title>
    <para>First paragraph.</para>
    <para>Second paragraph.</para>
    <para>Third paragraph.</para>
  </sect1>
  <sect1>
    <title>Section Three</title>
    <para>First paragraph.</para>
    <para>Second paragraph.</para>
    <para>Third paragraph.</para>
  </sect1>
</article>

And two customization stylesheets, html.xsl:

<?xml version='1.0'?>
<xsl:stylesheet  
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:import
href="http://docbook.sourceforge.net/release/xsl/current/html/chunk.xsl"/>
  <xsl:param name="chunk.first.sections" select="1"/>
  <xsl:param name="chunk.fast" select="1"/>
  <xsl:param name="chunk.section.depth" select="3"/>
  <xsl:param name="suppress.navigation" select="0"/>
  <xsl:param name="generate.section.toc.level" select="3"/>
  <xsl:param name="toc.section.depth" select="3"/>
  <xsl:param name="shade.verbatim" select="1"/>
</xsl:stylesheet>

and xhtml.xsl:

<?xml version='1.0'?>
<xsl:stylesheet  
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:import
href="http://docbook.sourceforge.net/release/xsl/current/xhtml/chunk.xsl"/>
  <xsl:param name="chunk.first.sections" select="1"/>
  <xsl:param name="chunk.fast" select="1"/>
  <xsl:param name="chunk.section.depth" select="3"/>
  <xsl:param name="suppress.navigation" select="0"/>
  <xsl:param name="generate.section.toc.level" select="3"/>
  <xsl:param name="toc.section.depth" select="3"/>
  <xsl:param name="shade.verbatim" select="1"/>
</xsl:stylesheet>

1. For XSL stylesheets 1.64.1

When I use xsltproc and html.xsl everything is chunked correctly and I have
all navgational links (Prev/Next in header, Prev/Up/Home/Next in footer). 

However, with xhtml.xsl there is are no header navigation links and the
footer just has Up/Home.

2. For XSL stylesheets 1.68.1

html.xsl does not produce an "Up" footer link.

xhtml.xsl neither produces a "Prev"/"Next" nor an "Up" footer link.

I expected the same visual output for HTML and XHTML, at least for
stylesheets of the same version.

Cheers

Jens