Creating an admin-User named other than 'admin' fails

When I create an admin-User which is named alex, Arhiva behaves strangely.

I describe the screenshot steps (sorry it's in German but I'll translate)

1. I installed Archiva, went to localhost:8080 and pressed Create Admin User
2. I entered alex as username and saved
3. I got redirected to localhost:8282/#search with the message you have entered an invalid combination of username and password
4. When I tried to login again, I got the same message

Regards,
Alex