AWT/Swing layout behavior?

I am having trouble figuring out the right way to use the GridBagLayout =
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class.

I have some sample code (see below) that I _expected_ would take the two=
  =

components added to the frame and always make them the same size, arrang=
ed =

vertically.

What happens instead is that when one of the two components is a Panel o=
r =

JPanel (and possibly other container types...those are the two I tested)=
, =

if that component contains another component, it takes up more than half=
  =

of the frame.

Reading the documentation, I am under the impression that the =

GridBagLayout class automatically allocates the dimensions of a given =

component according to the weight assigned to it in the GridBagConstrain=
ts =

class set for the component. Thus, since these two components have the =
 =

same weights, they should always be equally sized. But for some reason,=
  =

having the container actually contain something affects this.

The sample code only adds one item, and the difference in size is =

noticeable but not very large. However, this came up in a more complex =
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situation, where a larger number of controls are added. In that case, t=
he =

size difference is proportionally larger as well, resulting in effective=
  =

relative weights more like 3 or 4 to 1.

Is there a way to get the GridBagLayout class, or some other built-in =

LayoutManager, to do this sort of auto-sizing where the relative weights=
  =

will always actually stay equal?

Thanks!
Pete

p.s. Something I ran into while putting the sample code together is tha=
t =

sometimes when I'd run the code, the button would not show up. It'd be =
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briefly visible, and it would show up again once the window is resized. =
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But to start with, it's not visible. Is there some basic flaw in the wa=
y =

I'm creating this UI that is leading to this erratic behavior? Or am I =
 =

just looking at some sort of run-time bug?

import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;

public class TestPanel
{

     /**
      * @param args
      */
     public static void main(String[] args)
     {
         Frame frame = new Frame("TestPanel");
         GridBagLayout grid = new GridBagLayout();
         GridBagConstraints constraints = new GridBagConstraints();
         JPanel panel;

         frame.setLayout(grid);

         constraints.fill = GridBagConstraints.BOTH;
         constraints.gridwidth = GridBagConstraints.REMAINDER;
         constraints.weightx = 1;
         constraints.weighty = 1;

         panel = new JPanel();
         panel.setBorder(new LineBorder(Color.BLACK));
         panel.add(new Button("Test"));
         frame.add(panel);
         grid.setConstraints(panel, constraints);

         panel = new JPanel();
         panel.setBorder(new LineBorder(Color.BLACK));
         frame.add(panel);
         grid.setConstraints(panel, constraints);

         frame.setSize(240, 480);
         frame.setVisible(true);
     }
}