i came with a better approach:

changing the listener from the form panel to the store, like this:
Code:
var storeOpcoesAcesso = Ext.create('Ext.data.JsonStore', {
...
groupField: 'descricao',
listeners: {
  load: function(este, opts) {
    groupingFeature.collapseAll();
  }
},
...
});
now its working fine