System freezes up after install requiring a manul shutdown of Virtualbox

[warren]

.VirtualBox 5
Ubuntu 16.04 Xenial Final 20160419
I assume this bug is similar to bug#1447038 except this is not a live session but a post install reboot problem.
Reboot after install does not work or freezes Virtualbox, requiring a manual shutdown of Virtualbox, then a manual start of the newly installed Ubuntu image.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: casper (not installed)
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Apr 19 21:52:13 2016
InstallationDate: Installed on 2016-04-20 (0 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160419)
SourcePackage: casper
UpgradeStatus: No upgrade log present (probably fresh install)

[Ubuntu QA Website (ubuntuqa)]

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1572387

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.