When a JFrame app is resized (enlarged) diagonally on Win32 it flickers a lot. This does not happen on horizontal or vertical resize.
You can use the following testcase to reproduce the problem:

import com.sun.java.swing.*;
import java.awt.*;
import java.awt.event.*;

public class TestApp extends JFrame
{
public TestApp() {
super("TestApp");

this.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent ev) {
System.exit(0);
}
});

JPanel panel = new JPanel(new BorderLayout());
panel.add(new JButton("West"), BorderLayout.WEST);
panel.add(new JButton("East"), BorderLayout.EAST);
panel.add(new JButton("North"), BorderLayout.NORTH);
panel.add(new JButton("South"), BorderLayout.SOUTH);
panel.add(new JButton("Center"), BorderLayout.CENTER);
this.setContentPane(panel);

this.pack();
this.setVisible(true);
}

public static void main(String[] args) {
new TestApp();
}
}