Software Updater fails to show packages that will be updated

[Forest]

When I logged in today, update-notifier told me that 6 updates were available. When I launched update-manager, the Software Updater window said "388kB will be downloaded", but the "Details of updates" list was empty.

There obviously were updates to be installed, as confirmed by the output of apt-get:
$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  apport apport-gtk python-apport python-problem-report python3-apport
  python3-problem-report
6 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 388 kB of archives.
After this operation, 1,024 B of additional disk space will be used.
Do you want to continue [Y/n]?

Despite the mysteriously empty Software Updater list, I clicked "Install Now", and the updates were installed. Still, I think it should have told me what it intended to install.

[Forest (foresto)]

I'm running Xubuntu 13.04 (raring) with update-manager 1:0.186.1.

[Launchpad Janitor (janitor)]

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

[Shiranami (akichi)]

I've had the exact same problem for the last three updates (that's around the same time this bug was posted). It's annoying not to know what I'm installing. I'm running Lubuntu 13.04 (raring), also update-manager 1:0.186.1.