Theming login form just for specific user registration / Auto Assign Role Page
You are rendering the user_login_block within your template, which is not rendered on the /user/login page.

As long as you have not placed a login-block, that you don't want to be affected, you should not have any problems.

You can use the template file block--user--login.tpl.php to theme this block or even use a form_alter hook to alter the form.