"No ID for constraint linkend" when using html/profile-docbook.xsl

Platform: Intel PIII,
	  debian sarge (testing/unstable)
	  xsltproc 1.0.33-3
	  docbook-xsl 1.62.4-1
	  docbook-xml 4.2-7

When processing mt documents with html/profile-docbook.xsl style
sheet, I see the error message like these:

Error: no ID for constraint linkend: customer_info.
Error: no ID for constraint linkend: billing_info.
XRef to nonexistent id: system_setup

I do not see these messages when processing with html/docbook.xsl.

Any clues?  customer_info and billing_info are id attributes on
<section> elements, while system_setup is an id attribute on an
<appendix> element.

Thanx!


- Steinar