Issue was when installing with an https:// base URL. This activated the cURL downloader code branch (more robust on https) which tried to access the config system for the proxy settings, but that was not yet initialised at that point in the installer.
function get_option()
{
debug_print_backtrace();
exit();
}
at the bottom of install.php, and tell me what that says when it was previously doing the reported issue, that should help.
Or if I can test directly on your server.