Software updater cannot be opened from launcher after resuming from standby

[Jeroen]

During normal operation the software updater might find new software. In that case the Software Updater icon becomes available in the launcher. After clicking the icon the Software Updater dialogue opens with an overview of new software.

However, this process doesn't work correct after a computer resumes from standby. If the Software Updater icon is available *directly* after resuming from standby, clicking on the icon does open the Software Updater dialogue, in fact it does nothing.
This issue is observed for more than a year now on Ubuntu 14.04 on *multiple* computers.

There are two workarounds to fix the situation, first is to reboot, the second is to right-click on the icon and quit Software Updater and then restart it manually from the Dash. However a non-technical user will not have a clue how to fix this.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: update-manager 1:0.196.13
ProcVersionSignature: Ubuntu 3.13.0-55.94-generic 3.13.11-ckt20
Uname: Linux 3.13.0-55-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Jun 27 11:55:40 2015
EcryptfsInUse: Yes
ExecutablePath: /usr/bin/update-manager
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'319'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'484'
 b'com.ubuntu.update-manager' b'launch-time' b'1435398928'
InstallationDate: Installed on 2014-04-18 (434 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
InterpreterPath: /usr/bin/python3.4
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)