Login bugs?

When I use WWF and login, if the username field was enter as: username or password, and whatever was enter for the password field, it then send me to the main login page instead of the error page.  When I try to register new username as "username" and "password" , it then tell me that these usernames had already been use.

Is there any way to prevent users to login forum and then type in "username or password" in the username field?

Thanks!