db2man: *roff macro incorrectly rendered, messes up man page

In the db2man stylesheet, whitespace in the ref page can cause groff 
macros to be indented, as in the following output:
==============================================
(1)

NAME
        sb-config - a tool used to determine compiler and linker flags

SYNOPSIS
            .ad l

        sb-config [option]

==============================================

Notice the indented .ad 1 macro line above, which causes it
to display verbatim in the man page.


Below is the source for the above example. If you remove the
leading spaces before <cmdsynopsis>, the .ad 1 line is
left-aligned and the man page renders correctly.

==============================================

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
"docbookx.dtd">
<refentry id="sb-config">
   <refnamediv>
     <refname>sb-config</refname>

     <refpurpose>a tool used to determine compiler and linker
     flags</refpurpose>
   </refnamediv>

   <refsection>
     <title>SYNOPSIS</title>

     <cmdsynopsis>
       <command>sb-config</command>

       <arg rep="norepeat"><replaceable>option</replaceable></arg>
     </cmdsynopsis>
   </refsection>
</refentry>

==============================================

I'm running with docbook.xsl 1.68.1 and saxon 6.4.3.