en-eclipse-plugin does not honour Eclipse sources as sources.
>
> In the Eclipse nomenclature the symbolic name of a source bundle is the
> symbolic name of the corresponding binary bundle suffixed with ".source".
> maven-eclipse-plugin:to-maven derives the groupId and a
f a source bundle is the
symbolic name of the corresponding binary bundle suffixed with ".source".
maven-eclipse-plugin:to-maven derives the groupId and artifactId from
the bundles symbolic name by taking the right part of the symbolic name
split by the last dot as artifactId and the left