SAPUI5: issue about function navButtonPress

i'm using SAPUI5 for a web site using Javascript method. Since version 1.28.9 of SAPUI5, using the function "navButtonPress" the web site go back to the previous page. From version 1.30, the "navButtonPress" function does not work anymore (it reloads the page and restarts the web site). This is a portion of code:

var pgDettaglioCliente = new sap.m.Page("pgDettaglioCliente", {  
    title: get("titleDettaglio"),  
    showHeader: true,  
    showNavButton: true,  
    navButtonPress: function () {  
        app.to("pgRiepilogoTicket");  
    },  
    content: new sap.m.Panel("pDettaglioCliente", {  
        content: [formDettaglioCli()]  
    })  
});

Any idea?

Thanks

Fabio