When a build contains tests that have failed, hudson marks the entire build as failed, which is a bit over the top if we look at the definitions on http://wiki.jenkins-ci.org/display/JENKINS/Terminology
So I think this is not the right behaviour, the result of the build should be 'unstable'. I can imagine this has something to do with the exit code of the grails command that is run by hudson. Is that what should be fixed? If so I will post an issue in the grails jira.