FULL PRODUCT VERSION :
jdk-1_5_0_08-windows-i586-p.exe
java version "1.5.0_08"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_08-b03
Java HotSpot(TM) Client VM (build 1.5.0_08-b03, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
XP2 SP2 all patches as of 22/09/06

EXTRA RELEVANT SYSTEM CONFIGURATION :
IDE:   Eclipse  Build id: M20060629-1905

A DESCRIPTION OF THE PROBLEM :

In a JFrame window using the X in the top of the window results in the 'finalize' method being called.

BUT.. when I try to close the window via a button, the 'finalize' method doesn't get called and it sits in memory. argh!

Have tested with the following JDK's

Code works with...
j2sdk-1_4_2_11-windows-i586-p.exe
jdk-1_5_0-windows-i586.exe
jdk-1_5_0_04-windows-i586-p.exe
jdk-1_5_0_06-windows-i586-p.exe
jdk-1_5_0_07-windows-i586-p.exe

FAILES WITH....
jdk-1_5_0_08-windows-i586-p.exe

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run attached code.

Click on button marked 'EXIT' and NO finalize statement is printed to system.out.

Click on 'X' button in the top right and it does print out that the finalize method is called.

Retest on previous JDK & it works. i.e. both X & 'EXIT' should print out that the finalize method is called.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
both X & 'EXIT' should print out that the finalize method is called.
ACTUAL -
Click on button marked 'EXIT' and NO finalize statement is printed to system.out.

Click on 'X' button in the top right and it does print out that the finalize method is called.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
None


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class CloseTest extends JFrame {
 
	JButton button;
	String name;
 
	protected void finalize() throws Throwable {
		super.finalize();
		System.out.println("finalize + CloseTest:" + name);
	}
	
	public CloseTest(String name) {
		this.name = name;
		setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
		button = new JButton("EXIT:"+ name);
		button.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e) {
				endEvent();
			}});
		addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				end();
			}
		});
		getContentPane().add(button);
		pack();
		setVisible(true);
	}
 
	private void endEvent() {
		dispatchEvent(new WindowEvent(this, WindowEvent.WINDOW_CLOSING));
	}
	
	private void end() {
		setVisible(false);
		dispose();
	}
	
	public static void main(String args[]) {
		
		new CloseTest("1");
		new CloseTest("2");
		new CloseTest("3");
		new CloseTest("4");
		new CloseTest("5");
		new CloseTest("6");
		new CloseTest("7");
		new CloseTest("8");
		new CloseTest("9");
		new CloseTest("0");
		
		System.out.println("ready");
 
		while(true) {
			try {
				Thread.sleep(500);
				System.gc();
			} catch (InterruptedException e) {
			}
		}
	}
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Go back to the last JDK

jdk-1_5_0_07-windows-i586-p.exe

Release Regression From : 5.0u7
The above release value was the last known release where this 
bug was not reproducible. Since then there has been a regression.