To reproduce run mongod with --auth and open a fresh copy of the mongo shell and then:

> use admin
switched to db admin
> db.admin.find()
error: {
"$err" : "unauthorized db:admin lock type:-1 client:127.0.0.1",
"code" : 10057
}
> db.admin.runCommand("shutdown")
Thu May 05 11:57:01 DBClientCursor::init call() failed
Thu May 05 11:57:01 query failed : admin.$cmd

to: 127.0.0.1
Thu May 05 11:57:01 Error: error doing query: failed shell/collection.js:150
Thu May 05 11:57:01 trying reconnect to 127.0.0.1
Thu May 05 11:57:02 reconnect 127.0.0.1 failed couldn't connect to server 127.0.0.1
>

The shutdown command should have failed with the same error as the find.