cryptsetup password different from login password

Hey all

Can anyone explain why my cryptsetup password, required when I turn on my machine on, and my normal (superuser) login is different?

Bakground: This happened about a month ago. I changed my password through terminal, but when my machine turned off, it would not accept the new password, so I tried the most recent password and that worked. I have since changed the superuser password again, and still the old password for the cryptsetup remains.

Any thoughts?

Cheers