[Security] Last screen shows briefly on resume if laptop suspended with a fullscreen window

1. Open Chromium and go to youtube
2. Play a video
3. Suspend
4. Resume

What happens:
When the screen turns on the youtube video will be shown briefly and then the greeter will appear

This can be easily replicated with any window.

(fullscreen a terminal window and suspend)

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity-greeter 16.04.1-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-14.30-generic 4.4.5
Uname: Linux 4.4.0-14-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Mar 21 23:38:00 2016
InstallationDate: Installed on 2016-03-18 (3 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160313)
SourcePackage: unity-greeter
UpgradeStatus: No upgrade log present (probably fresh install)