The following test case, which was taken from the JDC comments for bug
  6257260: Memory leak on closing JFrame
shows a memory leak in XAWT in 5.0:

---- test begins -----
import java.awt.Button;
import java.awt.Event;
import java.awt.Frame;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class XtoolkitIconLeak extends Frame {

    static boolean S_allowIcon = true;

    static int S_offset = 100;
    boolean S_etype = true;
    Button S_b = null;
    byte[] S_bigDummyData = null;

    public XtoolkitIconLeak(String name, boolean etype /* if true then exit app on windowClose() */){
        S_etype = etype;
        setTitle(name);
        /*--------------------------------------------------------------
         * Under Solaris 10 X86 if we intall an ICON in the frame, GC fails
         * and we leak 5M per window iteration (e.g. new frame and close)
         * -Dawt.toolkit=sun.awt.X11.XToolkit
         * or
         * unsetenv AWT_TOOLKIT
         */
        Toolkit kit = Toolkit.getDefaultToolkit();
        Image icon = kit.getImage("1.gif");
        if (S_allowIcon) {
            setIconImage(icon);
        }
        /*--------------------------------------------------------------------*/
        if (S_etype == true) {
            // only the primary window has a new frame button
            setBounds(0,0,250,100);
            setLayout(new GridLayout(1,1));
            S_b = new Button("create new frame");
            add(S_b);
        }
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent we){
                dispose();
                doGC(4,"Frame.dispose()");
                if (S_etype == true) {
                    // only the primary window invokes an application exits
                    System.exit(0);
                }
            }
        });
        setVisible(true);
    }

    public void doGC(int passes, String activity)
    {

        Runtime rt = Runtime.getRuntime();
        for (int i = 0; i< passes; i++) {
            System.gc();
            rt.gc();
            rt.runFinalization();
        }
        long free = rt.freeMemory();
        long total = rt.totalMemory();
        long used = total - free;
        String sused = "" + used;
        while (sused.length() < 9) sused = " " + sused ;
        System.out.println("HEAP USED = " + sused + ", ACTIVITY = " + activity);
    }

    public boolean action(Event event, Object arg)
    {
        if (event.target.equals(S_b)) {
            doGC(4,"new Frame()");
            XtoolkitIconLeak popup = new XtoolkitIconLeak("new sub frame",false);
            S_offset = S_offset + 22;
            popup.setBounds(S_offset, S_offset, 250,100);
            popup.S_bigDummyData = new byte[1000*1000*5];
        }
        return true;
    }

    public static void main(String args[]){
        System.out.println("awt.toolkit="+System.getProperty("awt.toolkit"));
        if (args.length > 0 && args[0].equalsIgnoreCase("NOICON")) {
            XtoolkitIconLeak.S_allowIcon = false;
            System.out.println("Not installing icons on frame via Frame.setIconImage()");
        }
        XtoolkitIconLeak Xtest = new XtoolkitIconLeak("main frame",true);
    }
}
----- test ends -----

I can reproduce the leak on Solaris 10 with Xawt toolkit.
The bug is not reproducible on mustang.