Unable to add a prerequisite goal from an ant-based mojo

According to the documentation you should be able to add a prerequisite goal from an ant-based mojo using the following syntax:

<pluginMetadata>
<mojos>
  <mojo>
.
.
.
    <execution>
      <goal>some:goal</goal>
    </execution>
.
.
.
  </mojo>
</mojos>
</pluginMetadata>

But this does not work. There is no error when building the mojo, but the goal element is ignored. The problem seems to be related to the fact that PluginMetadataParser does not map the execution.goal property of Mojo when converting it to MojoDescriptor (in the asDescriptor method).