These problems DO occur with the command line (appears at the beginning, so I did not notice)
[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.vivoweb:vivo-installer-solr:war:1.9.0-rc1
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-clean-plugin is missing. @ line 120, column 21
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.vivoweb:vivo-installer-vivo:war:1.9.0-rc1
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-clean-plugin is missing. @ line 122, column 21
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]