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)

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

A DESCRIPTION OF THE PROBLEM :
When a JComponent overrides getPreferredSize() to return a value that differs from the inherent one, Box reserves space for this component in the layout based on this overridden size, yet the component is painted using the inherent size: ignoring this new value. The result is that the component's layout space allotment is inconsistent with the actual painted graphics.

In the included test case, preferredSize is overridden to return a larger value than the default would be. The Boxes reserve space for this new value, but the components are drawn as if all sized smaller, leaving empty space in the Box. It also shows that GridBagLayout and FlowLayout behave as expected.


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;

public class BoxTester {
    
    /**
     * Shows panels with different layouts, and equal child components,
     * rendering different results.
     */
    public static void main(final String[] args) {
        final JFrame frame = new JFrame("Box Tester");
        frame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        frame.setLayout(new GridBagLayout());
        
        final GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;
        frame.add(getGridBagPanel(), gbc);
        frame.add(getFlowPanel(), gbc);
        frame.add(getHorizontalBox(), gbc);
        frame.add(getVerticalBox(), gbc);
        frame.add(getDefaultHorizontalBox(), gbc); // Uses plain JLabels.
        
        frame.pack();
        frame.setVisible(true);
    }
    
    
    private static JPanel getGridBagPanel() {
        final JPanel gridBagPanel = new JPanel(new GridBagLayout());
        gridBagPanel.setBorder(
                BorderFactory.createTitledBorder("GridBagLayout"));
        gridBagPanel.add(new TestLabel("Label 1"));
        gridBagPanel.add(new TestLabel("Label 2"));
        gridBagPanel.add(new TestLabel("Label 3"));
        return gridBagPanel;
    }
    
    private static JPanel getFlowPanel() {
        final JPanel flowPanel = new JPanel();
        flowPanel.setBorder(BorderFactory.createTitledBorder("FlowLayout"));
        flowPanel.add(new TestLabel("Label 1"));
        flowPanel.add(new TestLabel("Label 2"));
        flowPanel.add(new TestLabel("Label 3"));
        return flowPanel;
    }
    
    private static Box getHorizontalBox() {
        final Box box = new Box(BoxLayout.LINE_AXIS);
        box.setBorder(BorderFactory.createTitledBorder("Horizontal Box"));
        box.add(new TestLabel("Label 1"));
        box.add(new TestLabel("Label 2"));
        box.add(new TestLabel("Label 3"));
        return box;
    }
    
    private static Box getVerticalBox() {
        final Box box = new Box(BoxLayout.PAGE_AXIS);
        box.setBorder(BorderFactory.createTitledBorder("Vertical Box"));
        box.add(new TestLabel("Label 1"));
        box.add(new TestLabel("Label 2"));
        box.add(new TestLabel("Label 3"));
        return box;
    }
    
    /**
     * This panel contains regular JLabels -- not TestLabels (below).
     */
    private static Box getDefaultHorizontalBox() {
        final Box box = new Box(BoxLayout.LINE_AXIS);
        box.setBorder(
                BorderFactory.createTitledBorder(
                        "Box With Normal Labels"));
        box.add(new JLabel("Label 1"));
        box.add(new JLabel("Label 2"));
        box.add(new JLabel("Label 3"));
        return box;
    }
    
    
    /**
     * A JLabel that overrides getPreferredSize with a constant value:
     * 120, 50
     */
    public static class TestLabel extends JLabel {
        
        public TestLabel(final String labelText) {
            super(labelText);
            setBackground(Color.ORANGE);
            setOpaque(true);
        }
 
 
        public synchronized Dimension getPreferredSize() {
            return new Dimension(120, 50);
        }
        
    }
    
}

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