Delay between native BackButton and a custom BackButton.

I'm create a TabGroup, and add many windows in this TabGroup, using Alloy.createController.

When I'm change of tab, is showed a native BackButton and few seconds after is showed a custom BackButton.

var tabGroup = Titanium.UI.createTabGroup();
var newTab = Titanium.UI.createTab();
var newWindow = Alloy.createController("mycontroller").getView();
 
var button = Titanium.UI.createButton({
          backgroundImage : "images/button_menu.png",
});
newWindow.leftNavButton = button;
 
newTab.window = newWindow;
tabGroup.addTab(newTab);
 
tabGroup.setActiveTab(1);

Titanium SDK: 3.4.0.GA

iOS Device: iPhone 4S