If you create a promotion for a job, and then navigate to the "Promotion Status" page, and then click on the promotion itself, you will see a "Build Now" button. If you click this button, you will see a build running in the Build History window with a "null" running and estimated time.

If you try to cancel the build, nothing will happen. If you go back to the Jenkins index page, you will not see the job running on an executor.

You will also see this exception in the logs: https://gist.github.com/recampbell/c00b90a6ffbbbb938198