Comment 3 for bug 975860

I think I have the same problem. In my case install of the flashplugin-installer 11.2.202.228ubuntu3 locks up in the following processes:

root 8599 8598 0 08:53 pts/1 00:00:00 apt-get install flashplugin-installer
root 8618 8599 0 08:53 pts/2 00:00:00 /usr/bin/dpkg --status-fd 47 --unpack --auto-deconfigure /var/cache/apt/archives/flashplugin-installer_11.2.202.228ubuntu3_i386.deb
root 8628 8618 0 08:53 pts/2 00:00:00 /bin/sh /var/lib/dpkg/info/update-notifier-common.postinst triggered /usr/share/package-data-downloads
root 8629 8628 0 08:53 pts/2 00:00:00 /usr/bin/python /usr/lib/update-notifier/package-data-downloader

If I kill the last process, the installation then completes as follows:

The following NEW packages will be installed
  flashplugin-installer
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/8,320 B of archives.
After this operation, 146 kB of additional disk space will be used.
Preconfiguring packages ...
Selecting previously unselected package flashplugin-installer.
(Reading database ... 199296 files and directories currently installed.)
Unpacking flashplugin-installer (from .../flashplugin-installer_11.2.202.228ubuntu3_i386.deb) ...
Processing triggers for update-notifier-common ...
http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_11.2.202.228.orig.tar.gz
Terminated
dpkg: error processing update-notifier-common (--unpack):
 subprocess installed post-installation script returned error exit status 143
No apport report written because MaxReports has already been reached
                                                                    Errors were encountered while processing:
 update-notifier-common
E: Sub-process /usr/bin/dpkg returned an error code (1)

Hope the above helps.