store does not refreshed in reconfigure extjs 4.1
var pagingBar = grid.getDockedItems()[1];
 pagingBar.unbind(store);

  store = Ext.create('Ext.data.Store', {
            fields: tmpFields,
            pageSize: itemsPerPage,
            proxy: {
                type: 'ajax',
                url: getDataWithPageURL,
                reader: Ext.create('CustomReader', { root: 'Results', totalProperty: 'Total' })
            }
        });


        store = store.load({
            params: {
                start: 0,
                limit: itemsPerPage
            }
        });


pagingBar.bind(store);