Comment 9 for bug 48682

Hi, I can confirm the problem also happens in the Ubuntu 7.04 and 7.10 with update-manager. The solution is also the one listed at the comment above:

$> export http_proxy="http://username:<email address hidden>:80"
$> sudo update-manager

I would like to suggest a possible solution.
Maybe, you can put a wrapper shell in order to start update-manager and that shell could extract the parameter from /root/.synaptic/synaptic.conf some variables and set the http_proxy only for the update-manager (or adept-manager) session.

Also, this bug seems duplicated with a lot of others. See:
bug #173050
bug #162996
bug #115388
bug #109700
bug #21536

Hope this helps.