the only way I actually managed to "correctly" update the drawing, is by drawing something over it, using:
graphics.setColor (getBackground ());
graphics.fillRect (0, 0, this.getSize().width, this.getSize().height);
supposed to clear the graphics and let space for the incoming?
basically destroys that particular graphics context, and any calls to it after are ignored.
Also, instead of setting the current color to the background color and fillRect, you can simply: clearRect()
That uses the background color (hence 'clear' as in wipe off) automatically.