Ext.TabPanel: event 'activate' not fired for first added tab

[fguest]

Press button "Add" twice. In console print info only for "Panel-2". After select "Panel-1" print info for "Panel-1".

P.S. In 4.0.7 for "Panel-1" event 'activate' fired twice for first activate...

var cnt = 0;
    var b_add = Ext.create('Ext.Button', {
      renderTo: document.body,
      text: 'Add',
      handler: function() {
        cnt++;
        var p = Ext.create('Ext.panel.Panel', {
          title: 'Panel-' + cnt,
          items: [
            {html: 'Text-' + cnt}
          ],
          listeners: {
            activate: function(a) {
              console.info("Activate", a);
            }
          }
        });
        panel.add(p);
        panel.setActiveTab(p);
      }
    });
    var panel = Ext.create('Ext.tab.Panel', {
      renderTo: document.body,
      width: 500,
      height: 300
    });