appcenter does not honor system proxy setting

living in a network behind a http proxy prevents appcenter from contacting repositories, no matter that you configure the proxy in system settings (which i fine for all other apps).

possible workaround: add a proxy setting in the apt config, e.g. add following line to /etc/apt/apt.conf.d/70debconf

Acquire::http::Proxy "http://192.168.2.1:8123";