The default for Debian Cinnamon when configured for manual username entry is a combined dialog box where the user enters their username and password in one combined dialog box.
When it does, the actual password can be logged as a username in a log file for a failed login attempt.
It can happen, especially if you accidentally 'typo' the initial login. It is easy to type the password in the username field by accident. After you enter the username, the dialog box goes away and the login greeter presents a second, separate dialog box for the password. When 'Hide the user list' is enabled on Linux Mint Cinnamon, the login greeter presents two separate login dialog boxes - first a dialog box to enter the username. A common display manager for login is LightDM, for example - look in /etc/lightdm/. In Linux Mint Cinnamon and some other distros, you can use the Login Window Setting application to change the login setting in the Users tab: Enable 'Hide the user list.' In other distros, you can configure it through a setting in the /etc directory. I have no justification other than 'minimize information leakage' or 'I just like it that way'. I prefer old way of asking the user to type their username rather than present the list of users on a platter for someone sitting down at the screen. Current desktop operating systems present a list of usernames for selection at login time.
