Maven Javadoc Plugin not finding custom taglets

Question

I created some custom JavaDoc Taglets as described here:

http://docs.oracle.com/javase/7/docs/technotes/guides/javadoc/taglet/overview.html

They work correctly with the Maven Javadoc Plugin when I manually specify the Taglets classes:

      <taglets>
        <taglet>
          <tagletClass>package.to.YourFirstTagletClass</tagletClass>
        </taglet>

        <taglet>
          <tagletClass>package.to.YourSecondTagletClass</tagletClass>
        </taglet>
        ...
      </taglets>

      <tagletArtifact>
        <groupId>group-Taglet</groupId>
        <artifactId>artifact-Taglet</artifactId>
        <version>version-Taglet</version>
      </tagletArtifact>

as described here: http://maven.apache.org/plugins/maven-javadoc-plugin/examples/taglet-configuration.html

But if I have the plugin auto-detect my Taglets as described at the end of the above link, i.e.:

      <tagletArtifacts>
        <tagletArtifact>
          <groupId>group-FirstTaglet</groupId>
          <artifactId>artifact-FirstTaglet</artifactId>
          <version>version-FirstTaglet</version>
        </tagletArtifact>
      </tagletArtifacts>

Then, when building, I get the following error:

[WARNING] Unable to auto-detect Taglet class names from '/path/to/jar.jar'. Try to specify them with <taglets/>.

Anyone has suggestions on what to check?

Thanks!