Strange effect in nabvar with IOS7

When I start the app the image of the navbar from home running, but if I navigate to another screen and back to the home of the navbar image makes a strange effect. Is it a bug?

W.Home = function(){
    var win = UI.Win({
        file:'home.js',
        barColor:'#FFFFFF',
        backgroundColor:'#F7DD00',
        color:'#000000',
        titleImage:'images/navbar-xxx.png',
        tabBarHidden:true,
    });