SFTP clients using the PuTTy authentication mechanism cause the "Unsupported protocol sequence" error

Hi,

Updated SFTP clients using the PuTTy authentication mechanism like WinSCP e Filezilla, cause the "Unsupported protocol sequence" error during authentication on Ubuntu 16.04 and proftpd-basic 1.3.5a-1ubuntu0.1

The bug was fixed in Proftpd 1.3.6 by the ProftpD team:.

http://bugs.proftpd.org/show_bug.cgi?id=4385

But it will not be fixed by them in Proftpd 1.3.5, which is the version used in Ubuntu 16.04 and 18.04, because it is no longer supported

The debian versions 8 and 9, still supported, also use ProFTPD 1.3.5 and they released a fix:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949622

Please, can we have this fix on Ubuntu 16.04 updates which is still supported?

More related links:
https://forum.filezilla-project.org/viewtopic.php?t=51875
https://winscp.net/forum/viewtopic.php?t=28469

Thank you.