Installer no longer working behind a proxy

All installers (from [1]) since qt-creator-opensource-linux-x86_64-4.6.0-rc1_1936.run from Feb. 15th or newer no longer work with a proxy, even when starting it with --no-proxy. It hangs with the message "Performing license pre-conditions check..." (see QTBUG-65143 and QTBUG-66463 ), and after that times out "Network connection not found. You can still continue installation." is shown and the installer can continue. The previous version ...-4.6.0-rc1_1935.run worked fine (and does not know the --no-proxy options). Was the installer built with a still buggy QtInstallerFramework?

1: https://download.qt.io/snapshots/qtcreator/4.6/