To change my 'main' password I do:
tab Password -> select 'Password: login' -> right mouse menu -> Change password
Then I enter previous password, and two times the new password.
After reboot, my new password is not valid: I have to enter the previous one!
More strange: I have updated my new one week ago.
In the beginning, after booting my laptop, I had to enter the new password.
But, suddenly, my new password was no more valid.
Then, my previous password was back!
And I cannot change it any more...
I use Ubuntu 12.04 in French
To change my 'main' password I do:
tab Password -> select 'Password: login' -> right mouse menu -> Change password
Then I enter previous password, and two times the new password.
After reboot, my new password is not valid: I have to enter the previous one!
More strange: I have updated my new one week ago.
In the beginning, after booting my laptop, I had to enter the new password.
But, suddenly, my new password was no more valid.
Then, my previous password was back!
And I cannot change it any more...