Chunked HTML DocBook output: footer differences between chunk.xsl and chunkfast.xsl

Hello,

I switched to "chunkfast.xsl" with DocBook XSL 1.76.1 and Apache Xalan, as per http://www.sagehill.net/docbookxsl/Chunking.html#FastChunking ... but I noticed that this made the "Previous" and "Next" links in the standard HTML footer disappear.  Switching back to "chunk.xsl" fixed the problem.

Is this a bug, a feature, or something I'm doing wrong?

Thanks,
Christopher