Maven-pdf-plugin: How to include nested items in pdf?

Question

I'm generating a pdf document from my maven site documentation using the maven-pdf-plugin. The documentation is written in Markdown.
Unfortunately the generated document does not include nested <item> tags.
For example, I have the the following content in my site.xml:

<menu name="Documentation">
  <item name="Sweets" href="sweets/sweets.html" collapse="true">
    <item name="Chocolate" href="sweets/chocolate.html"/>
    <item name="Bublegum" href="sweets/bublegum.html"/>
    <item name="Marzipan" href="sweets/marzipan.html"/>
  </item>
</menu>

In the resulting pdf I have the contents of sweets.html, but not the content of all the sub items.
I also tried using a pdf.xml file with the following content included:

<toc name="Table of Contents" depth="4">
  <item name="Sweets" ref="sweets/sweets.md">
    <item name="Chocolate" ref="sweets/chocolate.md"/>
    <item name="Bublegum" ref="sweets/bublegum.md"/>
    <item name="Marzipan" ref="sweets/marzipan.md"/>
  </item>
</toc>

Which gave me the same result.
Looking at the document model reference, it should be possible to nest <item> tags.

What am I doing wrong?

Here is some additional information:
Maven: 3.3.1
maven-pdf-plugin: 1.2
doxia-module-markdown: 1.6

Answer 1

Using maven-pdf-plugin Version 1.3 fixed the problem.