The ContactInfoForm has a next field to redirect to after the form is successfully completed. Unfortunately, that field is set to a max length of 40. It is pretty easy to get a url longer 40, which triggers a validation error on a hidden field, which isn't shown to the user.
It'd be nice if we could increase the max_length of that field to something larger. Maybe 200 or 300 or 1000?
The RegistrationForm also has a next field with a max_length, but this one is 100, and hasn't been a problem so far. If we decide to increase the next max_length > 100 we should change this one too.