Matching processing-instruction inside tgroup

I have a transform that imports 1.65/html/docbook.xsl and matches specific 
processing instructions.  It succeeds unless the processing instructions are 
located within a tgroup or child element. If I touch 1.65/html/table.xsl, I can 
access the processing-instruction value from the tgroup and tbody templates. I 
believe it is a precedence issue but can't locate the cause. Does someone know 
how to solve this?

I've included sample source below.

Thanks,

Lauren

##########################################
Message Output:
[xslt]     Custom PI outside table
[xslt]     Custom PI in table
[xslt]     docbook tgroup in tgroup
[xslt]     docbook body in tbody


XSLT Source:
<xsl:stylesheet 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
  version="1.0">

  <xsl:import href="../../../docbook-xsl/1.65/html/docbook.xsl"/>

  <xsl:template match="processing-instruction('Comment')">
    <xsl:variable name="comment" select="."/>
    <xsl:message>
    Custom PI <xsl:value-of select="$comment"/>
    </xsl:message>    
  </xsl:template>

</xsl:stylesheet>



XML Source:
<article>
  <title>test PI</title>
  <?Comment outside table?>
    <table frame="all" id="requestedtable">
    <title>title text</title>
      <textobject>
        <phrase>description</phrase>
      </textobject>
      <?Comment in table?>
      <tgroup cols="1">
          <?Comment in tgroup?>  
        <colspec colname="col1" colwidth="2*"/>
        <thead valign="top">
          <row>
            <entry>
              <phrase role="themebody">text</phrase>
            </entry>
          </row>
        </thead> 
        <tbody valign="top">
          <?Comment in tbody?>  
          <row>
            <entry namest="col1" nameend="col4">
              <phrase><emphasis role="bold">row</emphasis></phrase>
            </entry>
          </row>
        </tbody>
      </tgroup>
    </table>
</article>