ncorrect identification: line too long. The connection attempt was rejected. The server may be down, or your network may not be properly configured.
The proxy connection is controlled by a application named MacProxy, which I pre-define the HTTP CONNECT Proxy. Then All application should connect internet via the provided proxy server. I also tried to SSH to the same server in iTerm and Terminal. All of them could be successful, with MacProxy provided proxy.
I believe it's a bug of Cyberduck, and hope it could be fixed ASAP