iOS: Memory is not being released when a tab is removed from tabGroup

// create tab group

var tabGroup = Titanium.UI.createTabGroup();

// create base UI tab and root window

var win1 = Titanium.UI.createWindow({  

    title:'Tab 1',

    backgroundColor:'#fff'

});

var tab1 = Titanium.UI.createTab({  

    icon:'KS_nav_views.png',

    title:'Tab 1',

    window:win1

});

var label1 = Titanium.UI.createLabel({

    color:'#999',

    text:'Remove Tab1',

    font:{fontSize:20,fontFamily:'Helvetica Neue'},

    textAlign:'center',

    width:'auto'

});

label1.addEventListener('click', function() {

    tabGroup.removeTab(tab1);

    label1 = win1 = tab1 = null;

});

win1.add(label1);

// create controls tab and root window

var win2 = Titanium.UI.createWindow({  

    title:'Tab 2',

    backgroundColor:'#fff'

});

var tab2 = Titanium.UI.createTab({  

    icon:'KS_nav_ui.png',

    title:'Tab 2',

    window:win2

});

var label2 = Titanium.UI.createLabel({

    color:'#999',

    text:'I am Window 2',

    font:{fontSize:20,fontFamily:'Helvetica Neue'},

    textAlign:'center',

    width:'auto'

});

win2.add(label2);

//  add tabs

tabGroup.addTab(tab1);  

tabGroup.addTab(tab2);  

// open tab group

tabGroup.open();