Window.setClosable(boolean) doesn't work after upgrading to latest version

Hello,
  I use window with spinner label to show the background activity. Unfortunatelly after migrating from 7.3.8 to 7.7.3, the x on the window is visible even if the setClosable(boolean) was called with false value:

public class Spinner extends Window {

    private static final long serialVersionUID = -6360464010191183766L;
    
    private final String HEIGHT = "10%";
    private final String WIDTH = "10%";

    public Spinner(){
        super();
        Label spinner = new Label();
        spinner.setSizeFull();
        spinner.addStyleName("spinner-label");
        spinner.addStyleName("spinner-window");
        
        VerticalLayout layout = new VerticalLayout();
        layout.setSizeFull();
        layout.addComponent(spinner);
        layout.setComponentAlignment(spinner, Alignment.MIDDLE_CENTER);
        
        setContent(layout);    
        center();
        setWidth(WIDTH);
        setHeight(HEIGHT);
        setClosable(false);
        setResizable(false);
        setDraggable(false);
        addStyleName("spinner-window");
    }

}

(see attached screenshot for result).

Is it bug? Or do I something wrong? Note, that with 7.3.8 the x was not visible.

Agata