Strange Swing错误：设置GridLayout参数会使我的JPanel消失

不知道我是否犯了新手错误，但是在我的JFrame中为JPanel创建GridLayout时更改row参数似乎导致另一个JPanel完全消失：

这是代码的精简版本：

• 在GridBug构造函数中，我设置了我的布局，并在BorderLayout.CENTER中放置了一个JPanel子类 . 这在我的原始代码中执行其他操作，但这里只是绘制一个框以显示它正在显示 .

• 以某种方式添加到BorderLayout.PAGE_END的底部面板的状态导致中心面板消失

• 特别是，将GridLayout行参数更改为更高的值会导致中心面板消失，较低的值工作正常

• 现在的代码在我的计算机上不起作用，如果我取消注释某些代码以减少行参数，或者如果我不添加JLabel或subPanels那么它可以工作......

我不知道我做错了什么：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GridBug extends JFrame{

    static class ImagePanel extends JPanel{

        @Override
        public Dimension getPreferredSize(){
            return new Dimension(200,200);
        }

        @Override
        public void paintComponent(Graphics g){
            super.paintComponent(g);
            System.out.println("Painting image panel...");
            g.setColor(Color.CYAN);
            g.fillRect(0, 0, getWidth(), getHeight());
        }
    }

    public GridBug() {

        setLayout(new BorderLayout());

        /*PROBLEM CODE HERE*/

        //add center image panel - does not appear depending on GridLayout settings in other panels
        ImagePanel centerPanel = new ImagePanel();
        add(centerPanel , BorderLayout.CENTER);

        //add bottom panel
        JPanel bottomPanel = new JPanel();
        add(bottomPanel, BorderLayout.PAGE_END);
        bottomPanel.setLayout(new GridLayout(6,0)); //doesn't work
//              bottomPanel.setLayout(new GridLayout(5,0)); //works

        JPanel subPanel = new JPanel();

        //if I pass more than 4 or so rows as param to gridlayout, 
        //then imagePanel is not displayed
        subPanel.setLayout(new GridLayout(4,0));    //doesn't work
//              subPanel.setLayout(new GridLayout(3, 0)); //works


        //if I don't add this label - works
        JLabel label = new JLabel("A Label:");
        subPanel.add(label);

        bottomPanel.add(subPanel); //if I don't add the subPanel it works fine

        /*END OF PROBLEM CODE?*/

        //set window params
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400,400);
        setLocationRelativeTo(null);
        setVisible(true);
    }   

    public static final void main(String[] args){
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new GridBug();
            }
        });
    }
}