title: EXTJS 4 sortInfo is not working in JsonStore
body: <pre><code>Ext.define('RouteSeqModel', {
      extend: 'Ext.data.Model',
      fields: [{name: '_id', type: 'number'}, {name: 'Route_Seq' , type: 'int'},'Location_Name','Location_ID','Route_ID']
  });
  
  var RouteSeqStore = Ext.create('Ext.data.JsonStore', {
      model: 'RouteSeqModel',
      storeId: 'RouteSeqStore',
      autoLoad: false,
      sortInfo: { field: "Route_Seq", direction: "ASC" },
      proxy: {
          type: 'ajax',
          url: 'get-routeseq.php',
          api: {
                  create: 'insert-routeseq.php',
                  update: 'update-routeseq.php',
              },
          actionMethods: 'POST',
          baseParams: {
                  _id : 0,
              },  
          reader: {
              type: 'json',
              idProperty: '_id'
          },
          writer: {
              type: 'json',
              id: '_id'
  
           }
      }
  });
  
  Ext.define('MyApp.view.MyGridPanelRouteSeq', {
      extend: 'Ext.grid.Panel',
      id:'MyGridPanelRouteSeq',
      alias: 'widget.mygridpanelrouteseq',
      renderTo: Ext.getBody(),
      height: window.innerHeight,
      width: window.innerWidth/2,
      title: 'Route Sequence Setting',
      sortableColumns: false,
      store: RouteSeqStore,
  
      columns: [
          {
              xtype: 'gridcolumn',
              width: 70,
              dataIndex: 'Route_Seq',
              text: 'Sequence'
          },
          {
              xtype: 'gridcolumn',
              width: 160,
              dataIndex: 'Location_Name',
              text: 'Location Name'
          }]
  })
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/NAnCU.jpg" alt="enter image description here"></p>
  
  <p>Sequence is read the data from Route_Seq, but the column is still not sorting yet.</p>
  
  <p>i have no idea how come the grid is still not sorting..why?</p>