Error in scp_send to Windows Hosts

I'm hopeful that this is PEBCAK but I can't seem to resolve it no matter what I try.
Any attempts to scp_send a file to a windows host seem to fail on anything other than a relative filepath with no directory structures, all other paths panic at runtime with value: Error { code: Session(-28), msg: "failed to send file" }'.

For example the following code works but it places 'remote' in $HOME of the user and literally includes the single tics in the filename:

    let tcp = TcpStream::connect("IP.ADDR.OF.HOST:22").unwrap();
    let mut sess = Session::new().unwrap();
    sess.set_tcp_stream(tcp);
    sess.handshake().unwrap();

    sess.userauth_password(r"DOMAIN\username", "DomainUserPassword").unwrap();
    
    let buf = std::path::PathBuf::from("remote");
    let mut remote_file = sess.scp_send(buf.as_path(),
                                       0o644, 10, None).unwrap();

    remote_file.write(b"1234567890").unwrap();
    remote_file.send_eof().unwrap();
    remote_file.wait_eof().unwrap();
    remote_file.close().unwrap();
    remote_file.wait_close().unwrap();

ANY other pattern passed fails with this error including paths expecting that relative path to remain true. Scp to the host works fine from both linux and windows terminals. I see in the Event Viewer logs that there is no authentication issue so I'm kind of at a loss.

Examples of other paths I have attempted and this list is not exhaustive:

/C:/remote
c:/remote
/c/remote
/C/remote
C:\\remote
c:\\remote
c\\remote
C\\remote
Downloads/remote
Downloads\\remote

Start with the provided Rust reproducer and the scp_send call, testing the listed Windows path forms against the behavior described. Compare these results with the working terminal scp behavior and determine what successful remote-path handling should look like; done means sending the file succeeds for supported Windows paths without a runtime error.