I always had the problem that the global proxy settings I set for Gnome weren’t recognised by
add-apt-repository. Therefore adding new repository from Launchpad was a pain in the neck.
I recently found the solution or at least a good workaround. It seems that the you have to export the proxy setting on the command line manually. However it still didn’t work, because of the really stupid mistake I made that Korny Sietsma explained so well
If you export the proxy settings first and then sudo the proxy settings aren’t visible any longer. Totally clear if you think about it… sigh
1 Defaults env_keep="http_proxy https_proxy"
Remember to set both the httpproxy and httpsproxy.