Im using iCloud password to log in and unlock the screen (System Preferences > Users and Groups). Yesterday iCloud password was changed using https://appleid.apple.com web-site (from my iPad). But my home iMac is still accepting old iCloud password to log in and unlock the screen. Why this happens? Looks like a security issue. Restarting iMac and logging out and then back in to iCloud does not solves the issue.