Whenever I install Ubuntu or Mint from behind a proxy, I find that the installation hangs during the timezone configuration phase. Figuring that it had to be related to the network, I restarted the install and selected "Try Ubuntu" instead of "Install Ubuntu". This boots me into a gnome-shell.
From there I updated the proxy settings to the values appropriate for my network and clicked on the "Ubuntu Install" icon on the desktop. The install still stalls around the "Copying Files" phase, grrrr.
Using a terminal, I can verify that the environment variables are correctly set to the proxy values, however, when I examine the environ file in the /proc/pid entry for the installer process, these proxy variables are not set.
Therein lies the problem, the installer is almost certainly invoked using the old environment variables and consequently, never gets to see the proxy settings.
I suspect the issue would be resolved if I could log out and log back in again, forcing the gnome-shell to reload but that isn't an option as the Ubuntu live configuration does not allow you to do this. I've got a workaround which I'm going to post here for others but any additional insight or more elegant solutions are welcomed.