DocBook assembly processing: "no namespace bound to prefix d" + 'info' element contents ignored

Hi there,
A (possibly embarrassing newbie) question regarding DocBook assembly
processing.

When I process an assembly document with assemble.xsl verison 1.78.1, I
get the following error:

d:assembly : no namespace bound to prefix d
d:structure : no namespace bound to prefix d
d:module : no namespace bound to prefix d
d:resources : no namespace bound to prefix d
d:resource : no namespace bound to prefix d
error
xsltCompileStepPattern : no namespace bound to prefix d
compilation error: file
/Users/graeme/Downloads/docbook-xsl-1.78.1/assembly/assemble.xsl line 42
element template
xsltCompilePattern : failed to compile 'd:info'

Seemingly, the only way to fix it is to add the namespace
'xmlns:d="http://docbook.org/ns/docbook"' to the top-level element. Am I
missing something, or is the stylesheet broken?

I'm using xsltproc on Mac OS X, version information as follows:

Using libxml 20708, libxslt 10126 and libexslt 815
xsltproc was compiled against libxml 20708, libxslt 10126 and libexslt
815
libxslt 10126 was compiled against libxml 20708
libexslt 815 was compiled against libxml 20708


Thanks,

Graeme