Timeout properties are ignored when connecting via a proxy

The problem is that we have a slow sftp server which takes some time to establish connection with. It may take up to 2 minutes to establish a connection, and after that it works fine. When connecting using various ftp-clients we increased timeout property and it worked for us.
However this does not work via the code. When trying to connect via a secured proxy - it seems that both
ConnectionInfo.Timeout and SftpClient.OperationTimeout have no effect and connection is terminated due to a timeout after ~27 seconds.
This seems to be an old issue with at least one other user facing it in 2015
http://stackoverflow.com/questions/34388446/c-sharp-renci-sshnet-sftp-client-connection-behind-proxy-timeout#comment72017745_34388446
For me it the same with Renci.SSH 2014 as well as with the latest version SSH.NET.2016.0.0

Thank you in advance for your consideration of the issue

まず、プロキシ接続で ConnectionInfo.Timeout と SftpClient.OperationTimeout がどのように処理されるかを追跡し、その後、低速な SFTP サーバーで報告された障害を再現します。設定した値にもかかわらず、接続が約 27 秒後に終了する理由を確認します。セキュアプロキシ経由で接続する際に、設定したタイムアウトが守られれば完了です。