FULL PRODUCT VERSION :
java version "1.6.0_19"
Java(TM) SE Runtime Environment (build 1.6.0_19-b04)
Java HotSpot(TM) Client VM (build 16.2-b04, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
After upgrading to SDK 6, update 19, some classes executing a Swingworker stopped from working, throwing no error in the console (Thread not executed).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
We started to see the problem just upgrading the jvm 6 to update 19

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
We expected no changes in functionality.
ACTUAL -
The thread invoked from a SwingWorker never executed.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "AWT-Windows" java.lang.IllegalStateException: Shutdown in progress
        at java.lang.ApplicationShutdownHooks.add(Unknown Source)
        at java.lang.Runtime.addShutdownHook(Unknown Source)
        at sun.awt.windows.WToolkit.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.SwingWorker;

public class Hilo extends SwingWorker<Object, Object>
{
	@Override
	protected Object doInBackground() throws Exception
	{
		System.out.println("Thread executing");
		return null;
	}
}

public class TestThread
{
	public static void main(String[] args)
	{
		System.out.println("1");
		Hilo h = new Hilo();
		h.execute();
		System.out.println("2");
	}
}

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

CUSTOMER SUBMITTED WORKAROUND :
import javax.swing.SwingWorker;

public class Hilo extends SwingWorker<Object, Object>
{
	@Override
	protected Object doInBackground() throws Exception
	{
		System.out.println("Thread executing");
		return null;
	}
}

public class TestThread
{
	public static void main(String[] args)
	{
		System.out.println("1");
		Hilo h = new Hilo();
		h.execute();
		System.out.println("2");
		try
		{
			Thread.sleep(1000);
			System.out.println("3");
		}
		catch(InterruptedException e)
		{
			e.printStackTrace();
		}
	}
}

Release Regression From : 6u18
The above release value was the last known release where this 
bug was not reproducible. Since then there has been a regression.