Cannot close update manager

[Colin Law]

On up to date Precise, opened Update Manager (no updates found), clicked Settings to check on Software Sources, then closed the sources window wothout making any changes. On attempting to close Update Manager nothing seems to happen and I am left with it on screen but not responding to anything, thought the window can be moved about. All buttons are greyed out except Close which is Orange greyed. The close X highlights when moused over (but is a black cross on grey background) but it does nothing obvious.

In System Monitor it is showing Sleeping, 38MiB, poll_schedule_timeout, Normal.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.7
ProcVersionSignature: Ubuntu 3.2.0-18.28-generic 3.2.9
Uname: Linux 3.2.0-18-generic i686
ApportVersion: 1.94.1-0ubuntu1
Architecture: i386
CurrentDmesg.txt: [ 55.914484] CIFS VFS: default security mechanism requested. The default security mechanism will be upgraded from ntlm to ntlmv2 in kernel release 3.3
Date: Thu Mar 8 13:31:12 2012
ExecutablePath: /usr/bin/update-manager
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20111129.1)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Colin Law (colin-law)]

I realise now that I had not actually closed the Software Sources dialog, though I thought I had, it was hidden behind another window. I was therefore trying to close the Update Manager whilst the Sources window was still open. I came back here to mark the bug as invalid but see that someone else has marked it as affecting them within minutes of me reporting it.
Unfortunately I killed update manager before realising, so I cannot absolutely confirm now that this is what happened.