I had added it to the Design Extender list by mistake.
adding that line will certainly make the error go away, but it wont fix the underlying problem.
the problem is that the login page is created without the Server Validation Behavior to validate the login form. but the validation show if behaviors _are_ added. the validation show if behaviors don't do any good with out the server validation behavior.
the true solution to remove the validation show if behaviors, apply the server validation behavior, then re apply the validation show if behaviors like previously suggested.