Extjs grouping grid editing is working for first group only and not working for other groups

Question

I am using ext4.2.1 library for my app. I have a grouping grid which id editable for a few columns and have paging as well. But when I go to editing, it works for only the first group and for the other groups editing wont give the editor.

Any ideas or is this a bug with ext?

Ext.define('myapp.view.reports.fg.meGrid', {
extend: 'Ext.grid.Panel',
fixed: false,
requires: 'Ext.grid.plugin.CellEditing',
plugins: [
    {ptype:'cellediting'}
],
alias: 'widget.megrid',
selModel: {
    preventFocus: true,
    mode: "MULTI"
},


initComponent: function(configParam) {

    var me = this;
    var editorHelper = myapp.util.audit.EditorHelper;
    me.initConfig(configParam);
    //this.store=Ext.create('myapp.store.report.CodeStore');    
    me.store = Ext.create('Ext.data.Store', {
        fields: this.fields,
        groupField: 'Cp
            type: 'ajax',
            url: 'index.cfm?fa=fg.d_meReport&isAjax=true&isExt4=1',
            reader: {
                type: 'json',
                root: 'rows',
                totalProperty: 'total'

            }
        },
        pageSize: 50,
        autoLoad: true
    });

    me.features = [{
        groupHeaderTpl: 'Cp: {name}({children.length} Claims)',
        ftype: 'grouping',
        startCollapsed: true
    }];
    /*me.listeners =  [{
                  afterlayout: function(){ 
                    groupingFeature.collapseAll();
                  }
                }]; */

    me.store.proxy.extraParams = this.filter;

    me.bbar = Ext.create('Ext.PagingToolbar', {
        displayInfo: true,
        store: me.store,
        //pageSize: 50,    
        displayMsg: 'Displaying topics {0} - {1} of {2}',
        emptyMsg: "No topics to display"

    });


    me.store.provider = me.provider;
    me.store.on("update", editorHelper.claimUpdateHandler, me.store);
    me.callParent(arguments);
}

});

Thanks, Sj