GridPanel fails to update inside TabPanel

I have a GridPanel that updates correctly inside a regular container by just changing data then calling store.load(). If I put the that GridPanel inside a TabPanel, change the data and call store.load() the GridPanel does not update. I'm aware of 'over nesting' but I don't think I'm doing that here as the GridPanel is placed directly into the grid.

Any ideas why it doesn't automatically update?

code:

function doMainScreen() {
  tabPanel = new Ext.TabPanel({
    activeItem: 0,
    autoRender: true,
    layout: 'fit',
    width: 1024,
    height: 768,
    layoutOnTabChange: true,
    items:[{
      id: 'tab1',
      items: [doGrid1()]
    }, {
      id: 'tab2',
      items: [doGrid2()]
    }]
  });
  return tabPanel;
}

function doGrid1() {
  store = new Ext.data.JsonStore({
    proxy: new Ext.data.HttpProxy({url: destURL}),
    root: 'root',
    fields: [开发者_运维知识库'field1', 'field2', 'field3'],
    autoLoad: true
  });

  // Create the data bound grid control
  gp = new Ext.grid.GridPanel({
    id: listId,

    ...
}