When you change a login Password, it does not change the keychain password for security reasons. You must go into Keychain Access and change the password there, also. I believe it used to inform you of that.
If you've forgotten the Keychain Password, then you must create a new keychain and set it as the login keychain.
Yes, that is what I was trying to explain.
By default, the keychain has the same password as the login. You can change the keychain password independent of the login. If you change the login password not from within the particular user's login, the keychain will not be changed.
If you change the password as you did, you must change the keychain password to the same if you want it to auto-unlock the keychain on login. If you don't, whenever you attempt to use the keychain, it will ask for the password to unlock.