JPanel that has no double buffering draws its components without cleaning previous screen. As a result of that, components from different JPanel can be seen at the same time.

To reproduce the problem, run the following test app.
The first tab has double-buffering panel while the second has non double buffering panel.
Test Procedure:
click first tab and second tab.

// Test app
import java.awt.*;
import java.awt.event.*;
import com.sun.java.swing.*;

public class Test extends JFrame{
    JScrollPane sp1, sp2;
    JPanel onePanel;
    JPanel otherPanel;
    JTabbedPane tp;

    // if the container panel has double-buffering, it works fine no matter what
    // children panels has double or non double buffering to draw their
    // components.
    public static JPanel bodyP = new JPanel(); // true

    public Test() {
        super("test");

        bodyP.setLayout(new BorderLayout());

        onePanel = new JPanel(true);
        onePanel.setLayout(new BoxLayout(onePanel, BoxLayout.X_AXIS));
        onePanel.add(new JButton("one"));

        otherPanel = new JPanel(false);
        otherPanel.add(new JButton("two"));

        tp = new JTabbedPane();
        tp.addTab("test-tab1", null, onePanel);
        tp.addTab("test-tab2", null, otherPanel);
        tp.setSelectedIndex(0);

        bodyP.add("Center",tp);

    }

    public static void main(String args[]) {
        WindowListener wl = new WindowAdapter(){
            public void windowClosing(WindowEvent event){
                System.exit(0);
            }
        };
        Test frame = new Test();
frame.setBackground(Color.lightGray);
frame.addWindowListener(wl);
frame.setSize(500,200);
frame.add("Center", bodyP);
        frame.show();
    }
}

// end of file.