fo:basic-Link does not work after using IFConcatenator.appendDocument

When using "fo:basic-link" with an external URL, Apache FOP only produces the expected PDF result if the PDF is produced directly.

If the goal is to append multiply documents into one PDF-File by using the Intermediate Format and then concatinating them by IFConcatenator.appendDocument, the links do not work any more.

e.g.
<xsl:element name="fo:basic-link">
<xsl:attribute name="external-destination"><xsl:value-of select="url('http://google.de')"></xsl:value-of></xsl:attribute>
Link to Google
</xsl:element>

Won't work with this code:
IFConcatenator concatenator = new IFConcatenator(targetHandler, null);

//Iterate over all intermediate files
for (int i = 0; i < files.length; i++)

{ Source src = new StreamSource(files[i]); concatenator.appendDocument(src); }

For know I fixed the problem for me by removing the override of the method getDocumentNavigationHandler in the embedded class IFPageSequenceFilter of IFConcatenator.