in this module you are using maven-bundle plugin 
https://github.com/brig/modeshape/blob/ba23e90f07bce9bec2f5b91c3e76855d8c643992/modeshape-schematic/pom.xml#L94
this plugin generates metadata in the JAR's manifest for OSGi.
When this plugin is configured wrong you can't use module with OSGi.

here is description for plugin:
http://felix.apache.org/site/apache-felix-maven-bundle-plugin-bnd.html#ApacheFelixMavenBundlePlugin%28BND%29-UsingthePlugin

and answers to your questions:
- there is no impact on builds, just fix jar metadata;
- yes, it produce regular JAR