run the following test program:

import javax.swing.*;
import java.io.*;
class test {
    public static void main(String[] args) {
	JFileChooser jfc = new JFileChooser();
	jfc.setFileSelectionMode(JFileChooser.FILES_ONLY);
	jfc.setDialogType(JFileChooser.SAVE_DIALOG);
	jfc.setMultiSelectionEnabled(false);
	int result = jfc.showSaveDialog(null);
	if (result == JFileChooser.APPROVE_OPTION)
	    {
          	File f = jfc.getSelectedFile();
		System.out.println("f: " + f);
                if (f == null) return;	
	    }
    }
}

When the jfilechoose pops up, enter a filename which does not exist in your file system.  hit save.

On tiger b33, getSelectedFile will return the entered filename correctly.
On tiger b35, getSelectedFile will return null.

I tried on both winXP and solaris.

Also, I got null pointer exception sometimes too when I run the test program on my solaris box:

capoon [scratch]% /net/koori.sfbay/p/jdk06/jdk/1.5.0/beta2/b35/binaries/solaris-sparc/bin/java test
Exception in thread "main" java.lang.NullPointerException
	at javax.swing.plaf.basic.BasicListUI.updateLayoutState(BasicListUI.java:1116)
	at javax.swing.plaf.basic.BasicListUI.maybeUpdateLayoutState(BasicListUI.java:1059)
	at javax.swing.plaf.basic.BasicListUI.getPreferredSize(BasicListUI.java:331)
	at javax.swing.JComponent.getPreferredSize(JComponent.java:1542)
	at javax.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.java:769)
	at java.awt.Container.layout(Container.java:1398)
	at java.awt.Container.doLayout(Container.java:1388)
	at java.awt.Container.validateTree(Container.java:1470)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validateTree(Container.java:1477)
	at java.awt.Container.validate(Container.java:1445)
	at java.awt.Window.pack(Window.java:487)
	at javax.swing.JFileChooser.createDialog(JFileChooser.java:772)
	at javax.swing.JFileChooser.showDialog(JFileChooser.java:708)
	at javax.swing.JFileChooser.showSaveDialog(JFileChooser.java:645)
	at test.main(test.java:9)