I am afraid I don't know the procedure of line break condition. I encountered this for the first time. A little help will be appreciated. beside the output is fine in bookmap condition
<!-- set the title -->
<fo:block xsl:use-attribute-sets="__frontmatter__title">
<xsl:choose>
<xsl:when test="$map/*[contains(@class,' topic/title ')][1]">
<xsl:apply-templates select="$map/*[contains(@class,' topic/title ')][1]"/>
</xsl:when>
<xsl:when test="$map//*[contains(@class,' bookmap/mainbooktitle ')][1]">
<xsl:apply-templates select="$map//*[contains(@class,' bookmap/mainbooktitle ')][1]"/>
</xsl:when>
<xsl:when test="//*[contains(@class, ' map/title ')]/@sub">
<xsl:value-of select="//*[contains(@class, ' map/title ')]/@sub"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="newline"/>
</xsl:otherwise>
</xsl:choose>
</fo:block>
<!-- set the subtitle -->
<xsl:apply-templates select="$map//*[contains(@class,' bookmap/booktitlealt ')]"/>
<fo:block xsl:use-attribute-sets="__frontmatter__owner">
<xsl:apply-templates select="$map//*[contains(@class,' bookmap/bookmeta ')]"/>
</fo:block>
</fo:block>