Cannot get MouseDown to work in HwndHost derived class

The events for the mouse can be called through C# via the interop using a delegate.

In C++/CLI:

public ref class GameWindow : public HwndHost
{
    delegate void func0();

    func0^        OnLeftMouseDown;
    func0^        OnRightMouseDown;
    func0^        OnMiddleMouseDown;
    func0^        OnMouseMove;

    IntPtr WndProc( IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, bool% handled )
    {
        switch( msg )
        {
            case WM_IME_SETCONTEXT:
                if( LOWORD( wParam.ToInt32() ) > 0)
                    SetFocus( mHWND );

                handled = true;
                return IntPtr::Zero;

            case WM_LBUTTONDOWN:
                OnLeftMouseDown();

                handled = true;
                return IntPtr::Zero;

            case WM_RBUTTONDOWN:
                OnRightMouseDown();

                handled = true;
                return IntPtr::Zero;

            case WM_MBUTTONDOWN:
                OnMiddleMouseDown();

                handled = true;
                return IntPtr::Zero;

            case WM_MOUSEMOVE:
                OnMouseMove();

                handled = true;
                return IntPtr::Zero;
        }

        handled = false;
        return IntPtr::Zero;
    }
};

In C#:

public partial class MainWindow : Window
{
    // Only important source displayed...

    private GameWindow mWindowWorld;
    private Point      mMousePos;
 
    private void Window_Loaded( Object sender, RoutedEventArgs e )
    {
        mWindowWorld = new GameWindow();
 
        mWindowWorld.OnLeftMouseDown   = Window_World_OnLeftMouseDown;
        mWindowWorld.OnRightMouseDown  = Window_World_OnRightMouseDown;
        mWindowWorld.OnMiddleMouseDown = Window_World_OnMiddleMouseDown;
        mWindowWorld.OnMouseMove       = Window_World_OnMouseMove;
 
        Window_World.Child = mWindowWorld;
    }
 
    private void Window_World_OnLeftMouseDown()
    {
        // TODO: Perform desired actions here.
    }

    private void Window_World_OnRightMouseDown()
    {
        // TODO: Perform desired actions here.
    }

    private void Window_World_OnMiddleMouseDown()
    {
        // TODO: Perform desired actions here.
    }

    private void Window_World_OnMouseMove()
    {
        // Probably want to do something like this...
        Point mousePos = Mouse.GetPosition( mWindowWorld );
        mMousePos = new Point( mousePos.X, mousePos.Y );
    }
};

Although creating delegates is one solution, I ultimately ended up creating each mouse button function in the GameWindow class for code cleanliness. I then derived from that class, so I could keep the HwndHost separated from the main app.