Try setting the passwords to blank or empty entries. Keep in mind that I too see some inconsistencies in the user management area of Windows 8. I'm not writing it's right but that there is a problem in this area.

Managing your account appears in the full metro interface, creating a new user or dealing with another user uses a "windowed" interface and let's be frank. This was rushed to market. It may take a few more years to get fixed.
Bob