callout problems

Hi,

I have problems getting callouts to work properly in a programlistingco. I'm 
able to get the callouts beneath the programlisting with the explanatory 
texts ok, but I get no callouts up in the actual programlisting. This is how 
my docbook looks like:

                    <programlistingco>
                        <areaspec units="linecolumn">
                            <area id="x-co" linkends="x" coords="1 50" />
                            <area id="y-co" linkends="y" coords="2 50" />
                            <area id="z-co" linkends="z" coords="3 50" />
                        </areaspec>
                        <programlisting>
$ foo
$ bar
$ bleech
$ oink
                        </programlisting>
                        <calloutlist>
                            <callout arearefs="x-co" id="x">
                                <para>this is x</para>
                            </callout>
                            <callout arearefs="y-co" id="y">
                                <para>this is y</para>
                            </callout>
                            <callout arearefs="z-co" id="z">
                                <para>this is z</para>
                            </callout>
                        </calloutlist>
                    </programlistingco>

It is the same problem if generating html from the docbook.
These are the parameters I've been using with the stylesheets:

HTML: -param draft.mode yes -param callout.graphics 0 -param callout.unicode 1 
-param callout.extension 1
FO: -param paper.type A4 -param draft.mode yes -param callout.graphics 0 
-param callout.unicode 1 -param callout.extension 1

I've also tried "-param callout.graphics 1 -param callout.extension 1" for 
using graphics.
		    
I'm using Xalan and FOP 0.20.5. The FO is generated using the XSL stylesheets 
v1.64.1.

What am I doing wrong here?

/Per