await and Navigation.PushAsync()

Hello,
I want to do something like that:
1. User clicks on "New Thing" button. Navigation.PushAsync is called.
2. User enters some data and clicks "Submit" on New thing page. Navigation.PopAsync is called.
3. Code grabs data from page and something makes with it.

var toolbarItem = new ToolbarItem {
                Text = "New",
            };
            toolbarItem.Clicked += async delegate {
                var page = new NewThingPage ();
                await Navigation.PushAsync (page);  
                Debug.WriteLine ("**It should be called only after return from NewThingPage, but it always called before it. Why?**");
            };
            this.ToolbarItems.Add (toolbarItem);

Can somebody explain me why thread doesn't suspend execution at line with "await Navigation.PushAsync (page);"