seahorse resets sometimes the login keyring password

[olibre]

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...

Some of my tmp/cache directories are tmpfs:
  $ mount | grep -w tmpfstmp
  tmpfs on /tmp type tmpfs (rw,nosuid,noatime,size=10%,mode=1777)
  tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
  none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
  none on /run/shm type tmpfs (rw,nosuid,nodev)
  tmpfs on /var/tmp type tmpfs (rw,nosuid,noatime,size=10%,mode=1777)
  tmpfs on /var/log type tmpfs (rw,nosuid,nodev,noatime,size=10%,mode=0755)
  tmpfs on /var/log/apt type tmpfs (rw,nosuid,noatime,size=10%)

[olibre (olibre)]

I cannot reproduce it any more!

[olibre (olibre)]

This bug has just appeared again. I had to enter my initial password that corresponds to my login password :-(
I do not know why this behaviour occurs about once a month...

[olibre (olibre)]

Today, I has to enter my user password to unlock my login keyring.
The specific password I set for my login keyring on seahorse is not valid any more.
My first login keyring password was the same as my user password...