External monitor not enabled after wake from suspend

[Raphael Mankin]

The problem arises on my laptop when I have an external monitor connected through a kvm.

If I have only the external monitor enabled and the machine suspends, then on waking from the suspend, if the external monitor is *not* connected, neither monitor is enabled. The only way I have found out of this situation is to login on a tty and kill the session.

1 Login with both internal and external monitor
2. In xfce4-display-settings select only the external monitor (internal monitor is off)
3. Suspend the machine
4. At his point my kvm switches control to a different port and effectively disconnects the external monitor
5. Wake the machine and switch the kvm to use the external kbd and monitor
6. I can enter my password on the internal monitor but the unlock process leaves me with both monitors disabled.

If in xfce4-display-settings I select mirrored displays, the problem does not arise.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xfce4-settings 4.12.0-2ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-57.78-generic 4.4.35
Uname: Linux 4.4.0-57-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Jan 25 19:45:50 2017
InstallationDate: Installed on 2016-12-03 (53 days ago)
InstallationMedia: Xubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: xfce4-settings
UpgradeStatus: No upgrade log present (probably fresh install)