Problem with fop nesting tables

I seem to be having a problem in FOP nesting tables as follows:

<fo:table>    <!-- Outer Table -->
  <fo:table-column>
  ...
  <fo:table-body>
      <fo:table-header>
         <fo:table-row> ...
      </fo:table-header>
      <fo:table-row keep-together="always">
         <fo:table-cell>
            <fo:block>
                <fo:table>    <!-- Inner Table -->
                  <fo:table-body>
                    <fo:table-header> <!-- this gives error -->
                        ...
                    </fo:table-header>
                    <fo:table-row>
                        ...
                    </fo:table-row>

This xsl structure works. However as soon as I put in a table-header in the
inner table I get the following error:

[java] [ERROR] org.apache.fop.apps.FOPException: A table body must be
child of fo:table, not fo:table-body

Does anyone know if I am doing something wrong or is this a FOP bug?

Vincent