I kept wondering why Jenkins wanted to shut down when I got to work in the morning, and I finally spotted this in the logs:

Feb 02, 2016 6:32:03 AM org.jvnet.hudson.plugins.thinbackup.utils.Utils waitUntilIdleAndSwitchToQuietMode
INFO: Force quiet mode for jenkins now and wait unilt all executors are idle.

So I changed the ThinBackup settings and removed the checkbox concerning waiting/forcing idle. It saved the settings, but didn't seem to tell the running process/thread, because after canceling the "shutdown" from the GUI, it immediately tried again with the same log message.

Expected outcome: After telling it NOT to try to force an idle state, it should have stopped trying.

(Also, there's a typo in that INFO message.)