update-manager says there are updates and then says computer is already up to date

The notification icon on the panel indicates that there are updates. I click "view updates" and after a few seconds, a dialogue box declares the computer to be up to date. The notification icon is still there. I run apt-get update / upgrade in a terminal and updates are installed. The notification icon then disappears. Possibly a duplicate of Bug #35009 but I can't be certain.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: update-manager 1:0.186.2
ProcVersionSignature: Ubuntu 3.8.0-31.46-generic 3.8.13.8
Uname: Linux 3.8.0-31-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.9.2-0ubuntu8.3
Aptdaemon:

Architecture: amd64
Date: Fri Oct 11 08:32:38 2013
GsettingsChanges:
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'launch-time' b'1381498335'
InstallationDate: Installed on 2013-10-01 (10 days ago)
InstallationMedia: Xubuntu 13.04 "Raring Ringtail" - Release amd64 (20130423.1)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)