I haven't tested this yet, so if it ends up working please let me know. There is a Local Security Policy Setting, you may be able to control it via Group Policy, that enables the last logged on user to be displayed. See if that is enabled and if so, disable it and see if the issue persists. Not sure that fixes it but worth a shot.
Navigate to Local policies -> Security settings,"Interactive Logon: Hide last user..." and set it to activated, reboot the machine