DOCBOOK-APPS: no ID for linkend

[Gabor Hojtsy <goba at php dot net>]

Hi!

I just tried to build a CHM out of the PHP Documentation sources
using xsltproc, and I keep getting:

| Error: no ID for constraint linkend: funcref.
| Error: no ID for constraint linkend: langref.
| Error: no ID for constraint linkend: features.
| Error: no ID for constraint linkend: appendixes.
| Error: no ID for constraint linkend: language.basic-syntax.phpmode.
| ...

While the IDs are there of course. If I add any XML node with
any of these IDs, xsltproc first says I have duplicate IDs, and
then in the next step of the process says, there is no ID for
constraint linkend...

I have never experienced this kind of error, nor do I even think
about anything that can cause this. I have looked into the
stylesheet code, and seen, that a simple key() XPath call is used
to find the ID. I have also checked that the DTD is found and 
probably loaded in, so it should identify IDs as IDs (as the duplicate
ID error message also indicates)...
 
My question is how to overcome this issue? A major part of the links
in the PHP manual are missing if I process the manual this way...
Everything used to be all right, and I cannot remember that we
upgraded or changed the stylesheets...

Thanks for the answer in advance,
Gabor Hojtsy