Grid with editable Popup make fields readonly

Edit: I've tried DateTime formatting with:

@Html.Kendo().TextBoxFor(m => m.CreatedAt).Format("dd.MM.yyyy HH:mm:ss")

But it's not working - the output remains the same:

Fri Jul 31 2015 12:07:31 GMT+0200 (Mitteleuropäische Sommerzeit)

Thanks

Sven