I failed to reproduce this issue with OpenSSH, but I'm pretty sure this is not a SSH.NET issue:
See the section on "Running scp with talkative shell profiles on the remote side?" in https://blogs.oracle.com/janp/entry/how_the_scp_protocol_works.
See the section on "Running scp with talkative shell profiles on the remote side?" in https://blogs.oracle.com/janp/entry/how_the_scp_protocol_works.