I am using Dashboards 3.0.1, the latest released version. If I nagivate to the system settings page --> dashboard settings --> login page, and put "/public-dashboards/login.htm" into the input field, then press save, then logout, I am redirected to localhost:8080/public-dashboards/login.htm
If I navigate in my browser to localhost:8080/login.htm, I get the normal page and am not redirected.
If I navigate to localhost:8080, I am redirected to /publich-dashboards/login.htm
If I put in another string, such as "goodfellas.shtm" I will get the same behavior, except to localhost:8080/goodfellas.shtm.
What are you seeing? Can you keep an eye on your log when you press save if you have more trouble?