If a submodule of an m2 project is dereferenced, Hudson (very usefully) disables
the corresponding module job. However if the submodule is readded later, Hudson
does not re-enable the module job.

To be more concrete: say you have a POM with modules like so

<modules>
<module>foo</module>
<module>bar</module>
</modules>

If you were to remove "bar", Hudson would stop building the corresponding
artifact. If you added "bar" back later (without changing the group/artifact
ID), Hudson behaves as though it didn't notice.

A workaround is to edit the config.xml for the previously disabled module and
remove the <disabled>true</disabled> element, then tell Hudson to reread the
configuration from disk.