Maven Site Plugin: How does menu inheritance work?

Question

If I have a multi-module project, how can I inherit a menu from my parent POM? The project layout is:

main <-- main project which just contains modules
   parent   <-- parent POM
   ext      <-- 3rd party code

I tried this in my parent's site.xml:

<menu name="Projects">
   <item name="Main Project" href="${web-root}/" collapse="false">
      <item name="Parent POM" href="${web-root}/parent/" />
      <item name="3rd Party" href="${web-root}/ext/">
   </item>
</menu>

and in the site.xml of ext, I used:

<menu name="Projects" inherit="top" />

I get the menu but no links.

I also tried to define the menu in the main project's site.xml but the result is the same.