I found the root cause in the upstream bugzilla https://bugzilla.mindrot.org/show_bug.cgi?id=3872
- Bug#1117594: openssh-client: interactive session traffic... Francesc Zacarias
- Bug#1117594: closed by Debian FTP Masters <ftpma... Francesc Zacarias
- Bug#1117594: openssh-client: interactive session tr... Yves-Alexis Perez
- Bug#1117594: upstream bug Francesc Zacarias
