Processing instructions ignored in biblioentry and bibliomixed

[Xmplar <info@xmplar.biz>]

I have FO processing instructions to insert punctuation such as 
apostrophes and dashes. Typical PIs are:

<xsl:template match="processing-instruction('apos')">
<fo:character character="&#x2019;"/>
<xsl:apply-templates/>
</xsl:template>

<xsl:template match="processing-instruction('endash')">
<fo:character character="&#x2013;"/>
<xsl:apply-templates/>
</xsl:template>

These do not work for text that is within biblioentry or bibliomixed 
elements. Other combinations of elements do work, such as text in a 
<citetitle> element that is not nested in biblioentry or bibliomixed.
There is nothing in either of those templates that excludes processing 
instructions, so I'm wondering what else might be affecting this.