Unexpected XSL-FO formatting changes in versions of DocBook XSL after 1.65-1

Hello Everyone,

I am trying to upgrade a DocBook XSL customization layer used by a document whose formatting I thought I had settled using version 1.65-1 of the DocBook XSL stylesheets. Starting with version 1.66-0 and continuing with all subsequent versions of the DocBook XSL stylesheets up to 1.67-2, the formatted output controlled by the following changed: 

*****************************************
  <!-- font-family, font-size, and color of the chapter titles. Includes a matching colored rule beneath the chapter title text. -->
  <xsl:template match="title" mode="chapter.titlepage.recto.auto.mode">  
    <fo:block color="#336666" xmlns:fo="http://www.w3.org/1999/XSL/Format" 
           xsl:use-attribute-sets="chapter.titlepage.recto.style" 
           margin-left="{$title.margin.left}" 
           font-size="20pt" 
           font-weight="bold"
           font-style="italic"
           font-family="GillSans-BoldItalic"
           border-bottom-style="solid"
           border-bottom-width="3pt"
           border-bottom-color="#336666"
           space-after="9pt">
      <xsl:call-template name="component.title">
        <xsl:with-param name="node" select="ancestor-or-self::chapter[1]"/>
      </xsl:call-template>
    </fo:block>
  </xsl:template>
*****************************************

By "formatted output," I mean as rendered to PDF by FOP after running the DocBook XML through xsltproc. 

I've run some tests keeping the versions of xsltproc and FOP consistent.