It's the SGA (suppress go-ahead) negotiation that's necessary to avoid line mode.
Many telnet clients don't try to negotiate any telnet options if you connect to a non-standard port, because they assume that you're talking to something other than a telnet server, and that you therefore want an 8-bit transparent connection with local line editing. Examples would be to telnet to an SMTP server, FTP server, etc. for testing purposes. A telnet client that has that behavior but no provision for overriding it is defective, and should either be fixed, if possible, or deleted with prejudice.
