Why are grid sort options grayed-out?

[Nightwish]

Despite repeated efforts I've been unable to figure out why some of the columns in my grid have their sorting options (Sort Ascending, Sort Descending) grayed-out. Even if I wanted to disable them I wouldn't know where to go and do it...

Here's my grid setup - when the grid renders, only the ID and Title columns have sorting disabled:

    initComponent: function ()
    {
        EpisodeGrid.superclass.initComponent.call(this);
        this.configureEpisodeGrid();
    },

  configureEpisodeGrid: function ()
  {
    // replace the grid view config
    this.viewConfig =
    {
      emptyText: 'No episodes found.',
      forceFit: true,
      enableRowBody: true,
      narrativeMode: 'full',
      getRowClass: this.getNarrativeRowClass
    };

    // setup grid column model config, including the RowActions column
    this.getColumnModel().setConfig([
    {
      xtype: 'gridcolumn',
      header: 'ID',
      dataIndex: 'ID',
      width: 75,
      resizable: false,
      fixed: true,
      id: 'EpisodeID'
    }, {
      xtype: 'gridcolumn',
      header: 'Title',
      dataIndex: 'Title',
      id: 'EpisodeTitle'
    }, {
      xtype: 'gridcolumn',
      header: 'WFO',
      dataIndex: 'WFO',
      sortable: true,
      width: 75,
      hidden: true,
      resizable: false,
      fixed: true,
      id: 'WFO'
    }, {
      xtype: 'gridcolumn',
      header: 'Begin Date',
      sortable: true,
      width: 100,
      fixed: true,
      dataIndex: 'BeginDateTime',
      id: 'BeginDateTime'
    }, {
      xtype: 'gridcolumn',
      header: 'End Date',
      sortable: true,
      width: 100,
      fixed: true,
      dataIndex: 'EndDateTime',
      id: 'EndDateTime'
    }, {
      xtype: 'actioncolumn',
      header: '',
      width: 30,
      resizable: false,
      fixed: true,
      menuDisabled: true,
      items: [
      {
          iconCls: 'iconDeleteAction',
          tooltip: 'Delete Episode',
          handler: this.handleDeleteColumnClick,
          scope: this
      }]
    }]);

        // assign a new selection model with a single row select and add a listener
        this.selModel = new Ext.grid.RowSelectionModel({ singleSelect: true });
        this.getSelectionModel().on('rowselect', this.onEpisodeGridRowSelect, this);

        // add grid listeners
        this.on('rowdblclick', this.onEpisodeGridRowDblClick, this);

        // add EpisodeStore listeners
        this.store.on('beforeload', this.onEpisodeStoreBeforeLoad, this);
        this.store.on('datachanged', this.onEpisodeStoreDataChanged, this);
  },

Anyone have a hint or two on what's going on here?

[Nightwish]

I found it and it almost poked out an eye: "sortable: true" needs to be explicitly defined for every grid column.

[plalx]

I did not verify, but I think you can change the default to sortable: true using this code.

 
Ext.grid.Column.prototype.sortable = true;