Does not shutdown after accidental removal of crypto disk

When accidental removal of crypto disks (LUKS), i.e. USB ones, happens Ubuntu does not shut down.

The console log you find when pressing ESC during shutdown shows the waiting for the hung processes for 1 minute and 30 seconds. After the processes are killed and stopping of tasks continue, you finally find "Reached target shutdown" and nothing more happens.

The computer never shuts down nor reboots, depending of your choice. The computer has hung.

Expected result is that the computer shuts down or reboots.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: upstart 1.13.2-0ubuntu13
ProcVersionSignature: Ubuntu 3.19.0-28.30-generic 3.19.8-ckt5
Uname: Linux 3.19.0-28-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.4
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Sep 23 19:07:06 2015
InstallationDate: Installed on 2015-07-12 (73 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
ProcKernelCmdline: BOOT_IMAGE=/vmlinuz-3.19.0-28-generic root=/dev/mapper/hostname--vg-root ro quiet splash vt.handoff=7
SourcePackage: upstart
UpgradeStatus: No upgrade log present (probably fresh install)
UpstartBugCategory: System
UpstartRunningSessionVersion: upstart 1.13.2
UpstartRunningSystemJobs:
 Error: command ['initctl', '--system', 'list'] failed with exit code 1: initctl: Name "com.ubuntu.Upstart" does not exist
UpstartRunningSystemVersion: Error: command ['initctl', '--system', 'version'] failed with exit code 1: initctl: Name "com.ubuntu.Upstart" does not exist