Image callouts and roles

I'm using role attributes and the docbook stylesheets (successfully) to use one image format when rendering to FO, and other when rendering to HTML (i.e. epub).

      <figure xml:id="foo"><title>Foo</title>

        <mediaobject>
          <imageobject role="fo">
            <imagedata fileref="images/DIT-local.pdf"/>
          </imageobject>

          <imageobject role="html">
            <imagedata fileref="images/DIT-local.png"/>
          </imageobject>

        </figure>

However I have a couple of images using callouts, and using roles like that doesn't seem to work:

          <screenshot>
            <mediaobject>
              <imageobjectco role="fo">
                <areaspec>
                  <area coords="50,443,129,463" xml:id="Setting_Up_init_user"/>
                </areaspec>

                <imageobject>
                  <imagedata fileref="images/MVC-DIT-structure.svg" scale="50"/>
                </imageobject>
              </imageobjectco>
          <imageobject role="html">

               <!--
                <areaspec>
                  <area coords="50,443,129,463" xml:id="Setting_Up_init_user"/>
                </areaspec>

                -->
        <imagedata fileref="images/MVC-DIT-structure.png" scale="50"/>
          </imageobject>
            </mediaobject>
          </screenshot>

The SVG is just a wrapper that references the similarly named PNG and then adds some callout bugs.

Rendering that to FO results in two images side-by-side. Not sure if that's a bug, or expected behaviour. It isn't what I want though.

However if I change the second imageobject to an imageobjectco, which seems the logical structure, the <area> is problematic - I have a single calloutlist that needs to refer to the "same" callout in either image. And I can't have two <area>s with have the same xml:id :-(

I hate image callouts! :-)

Is there a more correct way to organize my two alternate images?

Cheers,

Chris