core_user_get_users function problem

Hi everyone!

I'm trying to use get_users function from web services, but I'm having the following problem:

Isigned up a user(using core_user_create_users) and I can verify this user at Moodle User List(including his email)...but when I try to use the key=email and value equal to user email..I have the following answer:

object(stdClass)#2 (2) {
  ["users"]=>
  array(0) {
  }
  ["warnings"]=>
  array(0) {
  }
}

object(stdClass)#2 (2) {
  ["users"]=>
  array(1) {
    [0]=>
    object(stdClass)#3 (6) {
      ["id"]=>
      int(5)
      ["fullname"]=>
      string(26) "testfirstname testlastname"
      ["firstaccess"]=>
      int(1419880151)
      ["lastaccess"]=>
      int(1419880151)
      ["profileimageurlsmall"]=>
      string(58) "http://192.168.2.126/moodle/pluginfile.php/31/user/icon/f2"
      ["profileimageurl"]=>
      string(58) "http://192.168.2.126/moodle/pluginfile.php/31/user/icon/f1"
    }
  }
  ["warnings"]=>
  array(0) {
  }
}

Why I can't see the email address from user?

I have tried core_user_get_users and get_users_by_fields..and I've the same problem.

I'm testing in Moodle 2.8.

Thanks!