This was one of the problems the BETA program uncovered and it will be fixed in the final version.
In the meantime, you can fix it by importing a registry file.
Save the following text into a file with a .reg extension and import it by executing it. After a reboot. the new user account should disappear.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList]
"BLINK_"=dword:00010000