<partintro> deletes part TOC

I was testing an FO customization to remove a part toc title by
    setting 'part toc' in template generate.toc, and wasn't able to. I
    have the customization in TDG (page 210) to add a toc to the part
    title page, plus I have my own customization to set the order of
    <partintro> and the part toc on recto and verso pages. I then
    tested output using the standard 1.78.0 stylesheets without
    customization. 

    For the first part title page, I have a partintro:

    <part>

        <title>Part 1 title</title>

        <titleabbrev>Part 1 abbrevtitle</titleabbrev>

        <subtitle>The part subtitle goes here...</subtitle>

        <partintro>

          <title>Part introduction title goes here
    (optional)...</title>

          <subtitle>Part introduction subtitle goes here
    (optional)</subtitle>

          <info>

            <authorgroup>

              <author>

               
<personname><firstname>Andrew</firstname><surname>Walker</surname></personname>

                <contrib>Senior Researcher</contrib>

              </author>

              <author>

               
<personname><firstname>Brian</firstname><surname>Charleston</surname></personname>

                <contrib>Junior bottlewasher</contrib>

              </author>

            </authorgroup>

          </info>

          <para>An introduction to the part can be put into para
    elements. </para>

          <mediaobject>

            <imageobject>

              <imagedata fileref="images/redlettucelogo.png"
    width="60mm"/>

            </imageobject>

          </mediaobject>

          <para>An introduction (again) to the part can be put
    into para elements. </para>

          <para>Further info for part titlepage goes
    here...</para>

        </partintro>

        <xi:include href="">

          <xi:fallback>

            <para>

              <emphasis>FIXME: MISSING XINCLUDE CONTENT
    chap1</emphasis>

            </para>

          </xi:fallback>

        </xi:include>

      </part>

    

    Using the standard stylesheets, I don't get a part toc generated.
    However, for the second part title page I don't have any additional
    content:

    <part label="2">

        <title>Part 2 title</title>

        <titleabbrev>Part 2 abbrevtitle</titleabbrev>

        <xi:include href="">

          <xi:fallback>

            <para>

              <emphasis>FIXME: MISSING XINCLUDE CONTENT
    chap2</emphasis>

            </para>

          </xi:fallback>

        </xi:include>

        <xi:include href="">

          <xi:fallback>

            <para>

              <emphasis>FIXME: MISSING XINCLUDE CONTENT
    chap3</emphasis>

            </para>

          </xi:fallback>

        </xi:include>

      </part>

    

    This does produce a part toc. What would be stopping the part toc
    from generating where there is partintro?

    

    
-- 

      Dave Gardiner