Multiple bibliographies - FOP error because of non-unique ids

[Jürgen Klein <dev@sntl-publishing.com>]

Hi,
we use DocBook xsl-stylesheets (1.72.0), xalan (2.6.0) and fop fop-0.94.
Therewith we try to generate PDF from DocBook-article within multiple
bibliography-elements. In source-xml, we have empty bibliomixed-elements
with id-attributes:
<article>...
<section id="first">...
<bibliography>
<bibliomixed id="DOC2008"/>
</bibliography>
...</section>...
<section id="third">...
<bibliography>
<bibliomixed id="DOC2008"/>
</bibliography>
</section>...
</article>

Bibliography entries are pulled in by bibliomixed-id from a separate
DocBook-bibliography-database (DocBook-document with a collection of
bibliography entries). Ids in the DocBook-bibliography-database are unique.
Ids in source-xml (DocBook-article) can't be unique (e.g.'DOC2008', see
above). Nevertheless, it's no problem to generate FO. While generating PDF
from this FO, FOP, unfortunately, causes an error: "Property id "DOC2008"
previously used; id values must be unique in document". 

Is there a way to get rid of this error? Is there another way to use
multiple bibliography-elements in DocBook and generate PDF, even though
bibliomixed-ids in source-xml can't be unique?

Thanks in advance,
Jürgen Klein