Software Updater Hangs when trying to use debconf

[Vindicator]

About halfway through, Software Updater hangs "Installing updates..."
I didn't have Details expanded to see where it hung.

journalctl contains some potential reasons for the hang:
Jun 03 12:21:18 - gnome-session[1678]: debconf: unable to initialize frontend: Gnome
Jun 03 12:21:18 - gnome-session[1678]: debconf: falling back to frontend: Dialog
Jun 03 12:21:18 - gnome-session[1678]: debconf: unable to initialize frontend: Dialog
Jun 03 12:21:18 - gnome-session[1678]: debconf: (TERM is not set, so the dialog frontend is not usable.)

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: update-manager 1:15.04.7
ProcVersionSignature: Ubuntu 3.19.0-20.20-generic 3.19.8
Uname: Linux 3.19.0-20-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Jun 3 12:27:27 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'788'
 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'1433351939'
InstallationDate: Installed on 2015-05-31 (2 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
InterpreterPath: /usr/bin/python3.4
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)