XSLT/FO issue -- id "x" already exists in this document

Greetings:

This is an issue that appears to have been addressed in the past, but 
which I am now seeing for the first time.

I have a substantial Docbook file, which is converted via xsltproc to 
both HTML and PDF.  I am having the
same problem with both docbook-xsl-1.62.0 and 1.62.4.  The Docbook 
conversion to HTML goes fine.

In the conversion to PDF, though, the conversion to FO works fine, but 
the mapping from FO to PDF produces:

[ERROR] file: ... id "id2908630" already exists in this document

 From ealier discussions in the list archives, it sounds like a similar 
problem was addressed already -- so now perhaps it
has regressed.  In my case, the trouble seems to be caused by a lengthy 
(49 items) list of qandaentries.  Does this
sound like a bug?  How much work is it to patch the stylesheets?

Many thanks in advance -- Mark Flood