REGRESSION: ssh plugin stopped working after upgrading to version 6.4.22

After upgrading fetchmail from version 6.4.21 to version 6.4.22, ssh stopped working.

I have this on my .fetchmailrc:

   poll my_server.org bad-header accept with proto IMAP auth ssh
	timeout	45
	plugin "ssh -a -2 -4 -x -q -C my_user@%h exec /usr/libexec/dovecot/imap -o mail_location=/home/my_user/dovemail/"
	folder INBOX
	mda "/usr/libexec/dovecot/deliver"

With version 6.4.21, it works perfectly:

  $ fetchmail my_server
  765 messages for my_user at my_server (folder INBOX).
  reading message my_user@my_server:1 of 765 (5716 header octets) (1232 body octets) flushed
  ...

But, after upgrading to 6.4.22, it stopped working:

  $ fetchmailrc my_server

  fetchmail: my_server: configuration requires TLS, but STARTTLS is not permitted because of authenticated state (PREAUTH). Aborting connection.  Server permitting, try --ssl instead (see manual).
  fetchmail: Socket or TLS error on my_user@my_server
  fetchmail: socket error while fetching from my_user@my_server
  fetchmail: Query status=2 (SOCKET)

A corresponding BZ was opened at Fedora bug tracker: https://bugzilla.redhat.com/show_bug.cgi?id=2008160