type: "string" column "is not valid date"

[GungFooMon]

I got this "string" column first_name, which seems to be validated (it doesn't even have a validation rule specified) in a grid.
When i open the edit popup and change it's value, i get a validation message: "first_name is not valid date"..
This does not happen if i remove the column birthdate or set it's type to be "string"...
In fact.. if i fill a valid date into first_name, and some random string into birthdate, it doesn't complain anymore.. so it seems that even tho birthdate is displayed as a datepicker, it tries to validate first_name.
This also only happens when the editable attribute is set to 'popup' and works with inline editing.
I am pretty amazed at how this can be possible. please help!!!

Code:

$(document).ready(function () {

    var crudServiceBaseUrl = '/participant',

    dataSource = source,

        batch: true,

        pageSize: 30,

        schema: {

            model: {

                id: "id",

                fields: {"id":{"editable":false,"type":"number","label":"ID"},"first_name":{"type":"string","label":"First Name"},"last_name":{"type":"string","label":"Last Name"},"birthdate":{"type":"date","label":"Birthdate"},"social_security_number":{"type":"string","label":"Social Security Number"},"smoker":{"type":"boolean","label":"Smoker"},"vegetarian":{"type":"boolean","label":"Vegetarian"},"miscelaneous":{"type":"string","label":"Miscelaneous"},"active":{"type":"boolean","label":"Active"},"blacklist_comment":{"type":"string","label":"Blacklist Comment"}}            }

        }

    });

 

    $("#grid").kendoGrid({

        dataSource: dataSource,

        width: 1000,

        toolbar: ["create"],

        columns: [{"title":"ID","field":"id"},{"title":"First Name","field":"first_name"},{"title":"Last Name","field":"last_name"},{"title":"Birthdate","field":"birthdate"},{"title":"Social Security Number","field":"social_security_number"},{"title":"Smoker","field":"smoker"},{"title":"Vegetarian","field":"vegetarian"},{"title":"Miscelaneous","field":"miscelaneous"},{"title":"Active","field":"active"},{"title":"Blacklist Comment","field":"blacklist_comment"},{"command":"destroy","filterable":false},{"command":"edit","filterable":false}],

        editable: "popup",

        selectable: "row",

        pageable: true,

        sortable: true,

        groupable: true,

        filterable: true,

    });

});