Comment 3 for bug 1322567

Yes, it's a setting change, though not sure it's a bug or a fix. Because according to the OpenSSH manual page:

http://www.openssh.com/cgi-bin/man.cgi?query=sshd_config

The default option in /etc/ssh/sshd_config for PermitRootLogin is yes, and in our settings it's without-password.

After a little bit more search, I found this description regarding to it:

https://launchpad.net/ubuntu/trusty/+source/openssh/1:6.6p1-1

In Changelog it says:

 * Change to "PermitRootLogin without-password" for new installations, and ask a debconf question when upgrading systems with "PermitRootLogin yes" from previous versions (closes: #298138).

Looks like it's a update / fix.