Using a JobDSL script to generate a multibranch Pipeline job does not trigger a branch index to find Jenkinsfile

Here is a simple dsl job

multibranchPipelineJob(repo) {
  branchSources {
    github {
      scanCredentialsId(credentials)
      repoOwner(credentials)
      repository(repo)
    }
  }
}

Using this created the job fine but did not trigger a branch scan until I manually triggered a branch index. It also works if you open the multibranch job configuration and save it with no changes.

Creating a multibranch job directly from the UI works fine.

The only way I can trigger a branch index is to add a triggers section to the command to periodically scan every minute. I then had to create 3 build steps:

1. JobDSL to create mutlibranch Pipeline job with a trigger set to 1 minute
2. Shell step to Sleep for 60 seconds
3. JobDSL to modify the multibranch Pipeline job and turn off the trigger.