As already discussed in https://groups.google.com/d/topic/job-dsl-plugin/hCOem65Gpa8/discussion:

Minmal example:

folder('foo') {
  primaryView 'bar'
}

listView("foo/bar") {
  jobs {
      regex '.*'
  }
}

This is probably the simplest example of a folder, an additional listView in that folder, which SHOULD be set as the primary view in that folder. It works in testcases, generates the correct XML and is correct when run on a "fresh" Jenkins.

When run on a Jenkins instance where 'foo' already exists, the primary view is not updated...