I have a Raspberry Pi running Jessie that I'm using as a notification gateway.
If I SSH to it and change the user pi password, it appears to take and when I open a separate SSH session to it it requires the new password. I also create several new users, set their passwords and allow them to sudo with no password.
However, if I reboot I loose all that config changes, the new users and the user pi reverts to the default password, raspberry.
passwd enter old password:raspberry enter new password:<new password> re-enter new password:<new password>
Then initiate a new SSH using the pi user, prompts for password > enter NEW password, access granted
Initiate SSH using user pi, password prompted > raspberry, access granted