WPF Cannot unsubscribe from a RoutedEvent, not working. After unsubscribing it continues firing

Question

I have an WPF User control in which I create a RoutedEventHandler. I want to raise an event notifying every time its height changes:

Wpfusercontrol.designer.cs:

public partial class Wpfusercontrol: System.Windows.Controls.UserControl
{
    public static readonly RoutedEvent HeightChangedEvent = EventManager.RegisterRoutedEvent(
            "HeightChanged", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(Wpfusercontrol));


    public event RoutedEventHandler HeightChanged
    {
        add { AddHandler(HeightChangedEvent, value); }
        remove { RemoveHandler(HeightChangedEvent, value); }
    }

    private void UserControl_SizeChanged(object sender, SizeChangedEventArgs e)
    {
       if (e.HeightChanged && HeightChangedEvent != null)
       {
           RaiseEvent(new RoutedEventArgs(HeightChangedEvent));
       }
    }
}

Then this WPF user control is hosted in an ElementHost

WindowsFormsHostControl.Designer.cs:

partial class WindowsFormsHostControl
{
        private void InitializeComponent()
        {
            this.ElementHostFormControl = new System.Windows.Forms.Integration.ElementHost();
            this.Wpfusercontrol= new Wpfusercontrol();
            this.SuspendLayout();
            // 
            // ElementHostFormControl
            // 
            this.ElementHostFormControl.Dock = System.Windows.Forms.DockStyle.Fill;
            this.ElementHostFormControl.Location = new System.Drawing.Point(0, 0);
            this.ElementHostFormControl.Margin = new System.Windows.Forms.Padding(2);
            this.ElementHostFormControl.Name = "ElementHostFormControl";
            this.ElementHostFormControl.Size = new System.Drawing.Size(75, 78);
            this.ElementHostFormControl.TabIndex = 0;
            this.ElementHostFormControl.Child = this.Wpfusercontrol;
            // 
            // WindowsFormsHostControl
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.Controls.Add(this.ElementHostFormControl);
            this.Margin = new System.Windows.Forms.Padding(2);
            this.Name = "WindowsFormsHostControl";
            this.Size = new System.Drawing.Size(75, 78);
            this.ResumeLayout(false);

        }

        private System.Windows.Forms.Integration.ElementHost ElementHostFormControl;
        private Wpfusercontrol Wpfusercontrol;
}

WindowsFormsHostControl.cs:

public partial class WindowsFormsHostControl: System.Windows.Forms.UserControl
{
     private RoutedEventHandler heightChangedEventHandler;

     public WindowsFormsHostControl()
     {
            InitializeComponent();
     }

     public WindowsFormsHostControl(RoutedEventHandler heightChangedEventHandler) : this()
     {
            this.heightChangedEventHandler = heightChangedEventHandler;
            this.Wpfusercontrol.HeightChanged += this.heightChangedEventHandler;
     }  

     public void SubscribeHeightChanged()
     {
            this.Wpfusercontrol.HeightChanged += this.heightChangedEventHandler;
     }

     public void UnsubscribeHeightChanged()
     {
            this.Wpfusercontrol.HeightChanged -= this.heightChangedEventHandler;
     }
}

This WindowsFormsHostControl is embedded within an UI object called custom task pane which is kind of UI container for VSTO Outlook Add-ins. This custom task pane has a button to resize its height but it does not provide an event to catch it. So when you resize the height of that custom task pane, the height of the wpf user control changes as well, so through the routed event in the wpf user control I know when the custom task pane is resized and I catch the event.

Now from one class in my VSTO Outlook Add-in application (which in fact is a winforms app), I perform below things:

private WindowsFormsHostControl windowsFormsHostControl = null;

this.windowsFormsHostControl = new WindowsFormsHostControl(this.WpfUserControl_HeightChanged);

System.Windows.Fomrs.Timer t;

private void WpfUserControl_HeightChanged(object sender, System.Windows.RoutedEventArgs e)
{
   // Dome some stuff
   ...
   
   t = new System.Windows.Fomrs.Timer();
   t.Tick += new EventHandler(Update);
   t.Interval = 100;
   t.Enable = true;
}

private void Update(object sender, EventArgs e)
{
    // Some more stuf....
    ....

    // In below lines I update the height of the custom task pane (VSTO Outlook UI object) which in turn causes the WPF user control to resize its height as well. So then, I am trying to unsubscribe from the wpf routed event, then update the height for custom task pane, and finally subscribe again to the wpf routed event. I do this to prevent routed event in wpf user control fires again.
    
    this.windowsFormsHostControl.UnsubscribeHeightChanged();
    // here I update the height for custom task pane
    this.windowsFormsHostControl.SubscribeHeightChanged();
}

The problem is that it looks like the line:

this.windowsFormsHostControl.UnsubscribeHeightChanged();

is not working because the routed event in the wpf user control continues raising each time I execute the line of code between UnsubscribeHeightChanged and SubscribeHeightChanged.

So what am i doing wrong?