DOCBOOK-APPS: XSL 1.56.1: The id N400036F already exists in thisdocument

Hi list,
I get this error message from FOP 20.4 (with Xalan under Windows XP):
"The id N400036F already exists in this document"
This happens only with the new XSL release, 1.55 worked fine. And, it
happens only with large documents. 60 pages seems to be the magic number
of pages.
Sounds like a FOP bug to me and I post it there too.

Stephan