Custom components won't paint in JLayeredPane

Question

we're creating some school project in Java. What are we trying to do: there is JScrollPane as part of the GUI, containing JLayeredPane (let's say "MapPane"). MapPane contains the map of the country (on the bottom), which is JLabel with icon. This works great, MapPane is scrollable, everything ok.

Now, we want to add some more custom graphical elements extending class SpatialElement

every element extends class SpatialElement (simplified):

public abstract class SpatialElement extends JComponent{
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        // ...
        // ...
        paintElement(g2d);
    }

    public abstract void paintElement(Graphics2D g2d);
}

So for example element Polygon looks like (simplified):

public class Polygon extends SpatialElement{  // SpatialElement extends JComponent

    ...

    @Override
    public void paintElement(Graphics2D g2d) {

        // set color, stroke etc.
        // ...
        // prepare an array of coordinates and size (as required in drawPolygon method)

        // draw fill
        g2d.fillPolygon(x, y, size);

        // draw polygon
        g2d.drawPolygon(x, y, size);
    }
}

So when user adds a new graphical element, a method addSpatialElement is called (in MapPane):

public class MapPane extends JLayeredPane implements MouseWheelListener, MouseInputListener, Observer{

 //...

     public void addSpatialElement(SpatialElement element) {
         element.updateBounds(); // set bounds of newly created element
         spatialElements.add(element); // local storage of created elements

         add(element, JLayeredPane.DRAG_LAYER + getComponentCount()); // put the element into another (higher) layer
         validate();
         // ???
    }
}

I hope the code is simple but descriptive enough. The problem is, that even though newly created component is added into the MapPane (extended JLayeredPane), the element won't paint. First I thought that it's caused by wrong boundaries (computed in updateBounds method) but they are ok.

If I directly call element.repaintComponent(getGraphics()) after adding it into the MapPane, it paints the element, but after any interaction with the MapPane (e.g. resize of the window, etc.) the MapPane is repainted and so the object won't repaint.

How to force the MapPane to repaint all containing components on resize? Do I have to override default paintComponent method of the MapPane (so I would iterate through the object and call repaintComponent() on each of them)?

Or is there some better, not so tricky solution how to do it?

Thanks for your advice.