Webinterface only asks for password not username

I installed urbackup server 2.3.8 on a Win10 machine and created an admin user through the web interface.

Now, the web interface shows a login prompt asking only for a password (not a username). The HTML input for the username has

style="display: none;"

Am I overlooking a reason why this could be intentional or is this a bug?

This is intentional. As long as you only have one user, it is like this. As soon you have a second user, you have the normal behavior.