When removing last component from JTabbedPane and the component is also selected, BasicTabbedPaneUI will hold the reference (through visibleComponent) until UI is validated again. During this revalidation, component is also set to non-visible (although it was removed previously).
So, if someone uses tabbed pane, then empties it and saves the instance for future reuse, big troubles can occur - mnamely emory leaks and unwanted 'vanishing' of UI components.

The code to reproduce the bug is below (an also in attachment)

/*
 * JTabbedPaneError.java
 *
 * Created on 11. záøí 2000, 13:59
 */

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

/**
 *
 * @author dsimonek
 */
public class JTabbedPaneError extends java.lang.Object {

    /** Creates new JTabbedPaneError */
    public JTabbedPaneError() {
    }

    /**
    * @param args the command line arguments
    */
    public static void main (String args[]) {
        final JFrame frame = new JFrame("Tab test");
        final JTabbedPane tp = new JTabbedPane();
        final DebugLabel testLabel = new DebugLabel("TEST");
        
        tp.addTab("Test tab", testLabel);
        frame.getContentPane().add(tp);
        frame.setDefaultCloseOperation(3);

        // Widgets to add/remove testLabel
        final JButton button = new JButton("Move label from tabbed pane to top frame, remove whole tabbed pane");
        final JButton button2 = new JButton("Return tabbed pane to AWT hierarchy");
        button2.setEnabled(false);
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                tp.setSelectedComponent(testLabel);
                tp.removeAll();
                System.out.println("Is visible after remove: " + testLabel.isVisible());
                frame.getContentPane().remove(tp);
                frame.getContentPane().add(testLabel);
                button.setEnabled(false);
                button2.setEnabled(true);
                System.out.println("Now BasicTabbedPaneUI holds reference to our testLabel,");
                System.out.println("IN SPITE OF THE FACT THE LABEL WAS REMOVED");
            }
        });
        button2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                testLabel.setVerbose(true);
                // here, lines below is tabbed pane revalidated and disaster is coming :-)
                frame.getContentPane().add(tp, BorderLayout.WEST);
                frame.repaint();
                new Thread(new Runnable () {
                    public synchronized void run () {
                        try {
                            wait(1000);
                        } catch (InterruptedException exc) {}
                        System.out.println("Test label should still be visible, but is it really?: " + testLabel.isVisible());
                    }
                }).start();
            }
        });
        frame.getContentPane().add(button, BorderLayout.SOUTH);
        frame.getContentPane().add(button2, BorderLayout.NORTH);
        frame.pack();
        frame.show();
    }
    
    
    static class DebugLabel extends JLabel {
        boolean verbose = false;
        public DebugLabel (String name) {
            super(name);
        }
        public void setVisible (boolean state) {
            super.setVisible(state);
            if (verbose) {
                System.out.println("*******************");
                System.out.println("");
                System.out.println("Visibility changed to: " + state);
                Thread.dumpStack();
                System.out.println("");
            }
        }
        void setVerbose(boolean verbose) {
            this.verbose = verbose;
        }
        
        public Dimension getPreferredSize () {
            return new Dimension(300, 300);
        }
    }
    
}