Update Manager showed an update for... nothing

[Vadim Peretokin]

See attached screenshot - update manager showed an update while failing to list any packages.

Checking apt-get upgrade, it was only "libgksu2-0" that needed an update.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: update-manager 1:0.186.1
ProcVersionSignature: Ubuntu 3.8.0-29.42-generic 3.8.13.5
Uname: Linux 3.8.0-29-generic x86_64
ApportVersion: 2.9.2-0ubuntu8.3
Aptdaemon:

Architecture: amd64
Date: Wed Aug 28 09:01:45 2013
GsettingsChanges:
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'launch-time' b'1377644309'
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'481'
 b'com.ubuntu.update-manager' b'window-width' b'484'
InstallationDate: Installed on 2013-08-15 (11 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)