FULL PRODUCT VERSION :
java version "1.5.0_06"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode, sharing)

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

A DESCRIPTION OF THE PROBLEM :
After closing a JFrame that contains a JEditorPane, a reference to the frame is held. I have traced this reference using YourKit back to the new "styleSheet" instance variable of javax.swing.text.html.CSS. See this method (line 3234 of javax.swing.text.html.CSS):

    /*
     * we need StyleSheet for resolving lenght units. (see
     * isW3CLengthUnits)
     * we can not pass stylesheet for handling relative sizes. (do not
     * think changing public API is necessary)
     * CSS is not likely to be accessed from more then one thread.
     * Having local storage for StyleSheet for resolving relative
     * sizes is safe
     *
     * idk 08/30/2004
     */
    private StyleSheet getStyleSheet(StyleSheet ss) {
        if (ss != null) {
            styleSheet = ss;
        }
        return styleSheet;
    }

The reference will be held onto until this method is re-entered later.



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
This reproducible test case requires the YourKit profiler. It should be easy to adapt this test for another profiler.

Run the application (included below). Click on "Open Frame". Close the frame. Run GC if desired. Capture a memory snapshot. Notice that an instance of TestPanel$LeakingFrame remains. In YourKit, select the LeakingFrame class and show multiple paths from root (say 5). The following path is reported:

parent of javax.swing.JRootPane (#ffffcb13)
parent of javax.swing.JLayeredPane (#ffffc953)
parent of javax.swing.JPanel (#ffffcb11)
parent of javax.swing.JScrollPane (#ffffcb12)
parent of javax.swing.JViewport (#ffffc948)
parent of javax.swing.JEditorPane (#ffffc975)
this$0 of javax.swing.text.JTextComponent$InputMethodRequestsHandler (#ffffc569)
[5] of java.lang.Object[7] (#ffffc360)
listenerList of javax.swing.event.EventListenerList (#ffffc4a7)
listenerList of javax.swing.text.html.HTMLDocument (#ffffc56b)
this$0 of javax.swing.text.DefaultStyledDocument$StyleContextChangeHandler (#ffffc4a1)
[1] of java.lang.Object[3] (#ffffc353)
listenerList of javax.swing.event.EventListenerList (#ffffc491)
listenerList of javax.swing.text.StyleContext$NamedStyle (#ffffc566)
styles of javax.swing.text.html.StyleSheet (#ffffc96e)
styleSheet of javax.swing.text.html.CSS (#ffffcb27)
css of javax.swing.text.html.StyleSheet (#ffffcc2a)
defaultStyles of javax.swing.text.html.HTMLEditorKit (#ffff6525) [Class]

After a little analysis, it was clear to me that the culprit was the new styleSheet instance variable in CSS. This change was new in J2SE 5.0, which also explain why this problem does not occur in 1.4.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The frame should have been available for garbage collection after it was closed.
ACTUAL -
A reference to the frame was held.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class TestPanel extends JPanel {
    private static class LeakingFrame extends JFrame {
        public LeakingFrame() {
            super("Leaking Frame");
            add(new JScrollPane(new JEditorPane("text/html", "")));
            setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        }
    }

    public TestPanel() {
        super(new FlowLayout());
        JButton button = new JButton("Open Frame");
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                LeakingFrame f = new LeakingFrame();
                f.setSize(300, 300);
                f.setLocationRelativeTo(null);
                f.setVisible(true);
            }
        });
        add(button);
    }

    public static void main(String[] args) {
        JFrame f = new JFrame("Leak Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new TestPanel());
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Invoke the following in an event handler when the window closes:

new HtmlEditorKit().setStyleSheet(null)