When using Robot#createScreenCapture(...) on a HiDpi system the wrong area is captured. The issue occurs only if:
- the application runs on a HiDpi system
- the application is started with Webstart
- the system property 'sun.java2d.dpiaware' is set to 'false'

A simple test can be found below - you can also give it a try by executing http://www.jyloo.com/downloads/public/test/robotScreenTest.jnlp. When pressing the ScreenCaptureNow button a screen capture of the yellow rectangle is made and displayed in a new window. On a HiDpi system the captured area is wrong.
 
Test Case:
-----------------------------------
package test.robot;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JWindow;
import javax.swing.border.LineBorder;

public class RobotScreenTest extends JFrame{
  private Rectangle rect = new Rectangle(100, 100, 400, 300);
  
  public static void main(String[] args) throws Exception{
    EventQueue.invokeLater(new Runnable(){      
      @Override
      public void run(){
        new RobotScreenTest();        
      }
    });
  }

  public RobotScreenTest(){
    setLayout(new FlowLayout());
    
    add(new JButton(new AbstractAction("Screen Capture Now"){      
      @Override
      public void actionPerformed(ActionEvent evt){
        try{
          final BufferedImage screenshot = new Robot().createScreenCapture(rect);
          JPanel pane = new JPanel(){
            @Override
            protected void paintComponent(Graphics g){
              g.drawImage(screenshot, 0, 0, null);
            }
          };
          pane.setPreferredSize(rect.getSize());
          JFrame f = new JFrame();
          f.setTitle("ScreenCapture");
          f.add(pane);
          f.pack();
          f.setVisible(true);
        }
        catch (Exception e){
          e.printStackTrace();
        }                
      }
    }));
    add(new JLabel("Bounds: "+rect));
    
    setTitle(getClass().getSimpleName());
    setSize(400, 300);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);    
    
    JWindow w = new JWindow();
    JPanel p = new JPanel();
    p.setBackground(Color.YELLOW);
    p.setBorder(new LineBorder(Color.RED));
    w.setContentPane(p);
    w.setBounds(rect);
    w.setVisible(true);    
  }  
}