manage checkboxes with jquery and send those values in controller

inside razor view I have two checbox properties. They are mutually exclusive. When one is selected other is not and vice versa.

@Html.EditorFor(model => model.Before)
@Html.EditorFor(model => model.Start)

inside same view on dom ready I manage checkbox click

$('#Before').change(function () {
     if ($(this).is(":checked")) {
        $('#Start').attr('checked', false);
        return;
     }   
     $('#Start').attr('checked', true);
});

$('#Start').change(function () {
    if ($(this).is(":checked")) {
        $('#Before').attr('checked', false);
        return;
    }
    $('#Before').attr('checked', true);
});

further I'm creating js object which will be stringified and sent to the mvc controller

var myObj= {            
      Before: $("#Before").is(':checked'),
      Start: $("#Start").is(':checked')      
};

 alert("Is before checked: "+$("#Before").is(':checked'));
 alert("Is start checked: "+$("#Start").is(':checked'));
/* This returns always selected (correct) value  */

$.ajax({
          type: 'POST',
          traditional: true,
          contentType: 'application/json',
          url: '/Home/Manage',
          data: JSON.stringify({ model: myObj}),              
          success: function (data) { }
          },error: function () {
              alert('error');
          }
});

and I have viewmodel which represent this myObj which is sent to the controller

public class MyViewModel
{
   public bool Start { get; set; }
   public bool Before{ get; set; }
}
[HttpPost]
public ActionResult Manage(MyViewModel model)
{ 
}

Problem is following:

When Start is checked then I'm getting Start as checked and Before as non checked which is fine, but when Before is checked and Start is not than both are received inside controller in model as false.