background images in RTF - compilation failure

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 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)

...

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

Thank you all in advance!
Nancy