C# in WPF does not allow clicking another button after window states maximized

When I click on maximizebtn_Click and the form is maximized then loadbtn_Click doesn't click

private void maximizebtn_Click(object sender, RoutedEventArgs e)
        {
            // Set the window state to maximized
            if (WindowState == System.Windows.WindowState.Normal)
            {
                WindowState = System.Windows.WindowState.Maximized;
            }
            else
            {
                WindowState = System.Windows.WindowState.Normal;
            }
        }
		
private void loadbtn_Click(object sender, RoutedEventArgs e)
    {
        // Create OpenFileDialog
        Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();

        // Set filter for file extension and default file extension
        dlg.DefaultExt = ".stl";
        dlg.Filter = "STL Files|*.stl;";

        // Display OpenFileDialog by calling ShowDialog method
        Nullable<bool> result = dlg.ShowDialog();

        if (result == true)
        {
            // Open document
            string filename = dlg.FileName;
            openfile = filename;
        }
        ModelVisual3D device3D = new ModelVisual3D();
        device3D.Content = Display3d(openfile);
	//Add the ModelVisual3D to the Children property of the HelixViewport3D
        viewPort3d.Children.Add(device3D);
    }