Validation plugin, remote validation misuse or bug?

Validation plugin, remote validation misuse or bug?

Hi. I'm trying to do an ajax verification on the email field. The problem appears when the email field (on error, "email@example.com is already in use") is re-focused: the error message becomes malformed ("http://w/index.php?dispatch=auth.check_email is already in use").
Screenshots:
- input focused, email checked, the error message appears as expected:
 
- input refocused, without changing it's value, the error message is now malformed:

...after few research with firebug I've found that [object Object] is actually the rule 'object' (like below, {"url": "http://..", "type": "get"}) and not the error message itself.

I have the following code:
  1. JS:
  2. $(document).ready(function() {
    var registration_form = $("#registration-form").validate({
    rules: {
    email: {
    required: true,
    email: true,
    remote: {
    url: "http://w/index.php?dispatch=auth.check_email",
    type: "get"
    }
    }
    },
    messages: {
    email: {
    required: "Field required",
    minlength: "Field field",
    remote: jQuery.format("{0} is already in use")
    }
    }

    });
    $('#reset_registration_form').click(function() { registration_form.resetForm(); return false; });




















  1. PHP (http://w/index.php?dispatch=auth.check_email):
  2. echo User::email_exists($_REQUEST['email']) ? "false" : "true";
Any suggestions? Is this is bug or I just screw the plugin's configuration? Thank you :)