Jenkins with a troubled thinBackup configuration causes weird message: “Jenkins is going to shut down”

• http://stackoverflow.com/questions/26218018/jenkins-is-going-to-shut-down/26639029

Jenkins’s “quiet mode” is the state that cause Jenkins to display “Jenkins is going to shut down” in a yelling red bar on top of the page.

Q:What is Jenkins’s “quiet mode”?
A: It’s about quieting down Jenkins (in preparation for a restart) – no new build job will get accepted in this mode. This mode will get cleared, once Jenkins will have started anew.