Software Updater fails to lauch apt-listchanges

Steps to reproduce:

* Install apt-listchanges and configure
* Run Software Updater (or wait for automatic run)
* If there are no changes, no error occurs
* If there are changes, accept them
* Wait for download

What should happen:

* Once download is complete, apt-listchange output should appear (possibly asking for confirmation)
* Then installation of changes should continue

What happens instead:

* Once download is complete, error occurs when apt-listchange is called
* Installation continues successfully

Notes:

* My apt-listchanges config does *not* include asking for confirmation
* This works if I do an update from the command line using apt (apt-listchanges behaves as expected)
* Will post error message when problem recurs (next time I have a download)

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: update-manager 1:0.196.12
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.3
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Aug 8 12:42:47 2014
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'744'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'1301'
 b'com.ubuntu.update-manager' b'launch-time' b'1407494550'
InstallationDate: Installed on 2014-04-24 (105 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)
---
ApportVersion: 2.14.1-0ubuntu3.3
Architecture: amd64
CurrentDesktop: Unity
DistroRelease: Ubuntu 14.04
InstallationDate: Installed on 2014-04-24 (105 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
Package: apt-listchanges 2.85.13ubuntu2
PackageArchitecture: all
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Tags: trusty
Uname: Linux 3.13.0-32-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm bumblebee cdrom dip fuse lpadmin plugdev sambashare sandstorm sudo
_MarkForUpload: True
---
ApportVersion: 2.14.1-0ubuntu3.3
Architecture: amd64
CurrentDesktop: Unity
DistroRelease: Ubuntu 14.04
InstallationDate: Installed on 2014-04-24 (105 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
Package: apt-listchanges 2.85.13ubuntu2
PackageArchitecture: all
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Tags: trusty
Uname: Linux 3.13.0-32-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm bumblebee cdrom dip fuse lpadmin plugdev sambashare sandstorm sudo
_MarkForUpload: True