I have the following sample code that zooms each time a button is pressed:
XAML:
<Window x:Class="WpfApplication12.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Canvas x:Name="myCanvas">
        <Canvas.LayoutTransform>
            <ScaleTransform x:Name="myScaleTransform" />
        </Canvas.LayoutTransform> 
        <Button Content="Button" 
                Name="myButton" 
                Canvas.Left="50" 
                Canvas.Top="50" 
                Click="myButton_Click" />
    </Canvas>
</Window>
*.cs
public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    private void myButton_Click(object sender, RoutedEventArgs e)
    {
        Console.WriteLine("scale {0}, location: {1}", 
            myScaleTransform.ScaleX,
            myCanvas.PointToScreen(GetMyByttonLocation()));
        myScaleTransform.ScaleX =
            myScaleTransform.ScaleY =
            myScaleTransform.ScaleX + 1;
        
        Console.WriteLine("scale {0}, location: {1}",
            myScaleTransform.ScaleX,
            myCanvas.PointToScreen(GetMyByttonLocation()));
    }
    
    private Point GetMyByttonLocation()
    {
        return new Point(
            Canvas.GetLeft(myButton),
            Canvas.GetTop(myButton));
    }
}
the output is:
scale 1, location: 296;315
scale 2, location: 296;315
scale 2, location: 346;365
scale 3, location: 346;365
scale 3, location: 396;415
scale 4, location: 396;415
as you can see, there is a problem, that I thought solve by using Application.DoEvents(); but... it does not exist a priori in .NET 4.
What to do?