RTF doc. compilation failure due to valid XSL customizations

Hi folks,

I have a document (in A5 format) that can be flawlessly
compiled in PDF format, but fails in RTF. It seems that FOP 0.94 cannot
handle background images in <fo:block> elements when creating an
RTF file. The following API in my print.xsl has caused this problem:

<xsl:param name="chap.label.path"

  select="normalize-space(//bookinfo//imagedata[@role='chap_label']/@fileref)"/>

<xsl:attribute-set name="chap.label.properties">

  ...

  <xsl:attribute name="background-image">

    <xsl:call-template name="fo-external-image">

      <xsl:with-param name="filename" select="$chap.label.path"/>

    </xsl:call-template>

  </xsl:attribute>

  <xsl:attribute name="background-attachment">fixed</xsl:attribute>

  <xsl:attribute name="background-repeat">no-repeat</xsl:attribute>

</xsl:attribute-set>

FOP fails to place the chapter number on top of a background

icon. As I said, in PDF it works fine. 

When compiling RTF, I get the following error message:

WARNING: Ignored deferred event for org.apache.fop.fo.flow.RetrieveMarker@be49e0[@id=null]

May 27, 2009 4:11:44 PM org.apache.fop.render.rtf.RTFHandler startBlock

SEVERE: startBlock: null

May 27, 2009 4:11:44 PM org.apache.fop.cli.Main startFOP

SEVERE: Exception

java.lang.RuntimeException: Exception: java.lang.NullPointerException

        at org.apache.fop.cli.InputHandler.transformTo(InputHandler.java:217)

        at org.apache.fop.cli.InputHandler.renderTo(InputHandler.java:125)

        at org.apache.fop.cli.Main.startFOP(Main.java:166)

        at org.apache.fop.cli.Main.main(Main.java:197)

...

After upgrading FOP to version 0.95 the issue described further remained unresolved. Any ideas, folks?
Please advise!

Thank you a lot in advance!!!!

Nancy