For debugging purposes I was rendering frames to the offscreen image using their paint(Graphics) method as following:

Window w;
BufferedImage img = new BufferedImage(w.getWidth(), w.getHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics g = img.getGraphics();
w.paint(g);
g.dispose();

What I've observed, that on Windows 7 I'm getting different rendering of the same window. Please compare my screenshot and result of paint() method invocation. You can notice:
1. Checkboxes are rendered differently, there are rendering artefacts on their borders on the real screenshot.
2. Clipping is not enforced on some parts of the checkboxes when rendered using "paint" method to the offscreen buffer.