Originariamente inviato da valia
al max posta il tuo codice e si vede.
Mi fa molto strano che il set del tooltip annulli gli effetti del mouse listener
il problema penso che sia che con il settaggio del tooltip viene aggiunto un listener sul pannello(MOUSEMOTIONLISTENER).

comunque ecco il codice: (il metodo initCOmponents() è quello che genera automaticamente netbeans)
codice:
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JPanel;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

/*
 * NewJFrame1.java
 *
 * Created on 25-lug-2011, 16.46.06
 */
/**
 *
 */
public class NewJFrame1 extends javax.swing.JFrame {
JPanel cv;
    /** Creates new form NewJFrame1 */
    public NewJFrame1() {
        initComponents();
        cv=new JPanel();
        cv.setSize(jPanel1.getSize());
        jPanel1.add(cv);
        cv.setBorder(BorderFactory.createLineBorder(Color.yellow));
        jPanel1.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        jPanel1.addMouseListener(new MouseAdapter() {

            @Override
            public void mouseClicked(MouseEvent e) {
                System.out.println("ka");
            }
        });
        
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jButton1 = new javax.swing.JButton();
        jPanel1 = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setText("jButton1");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 100, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 100, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(288, Short.MAX_VALUE))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addGap(0, 167, Short.MAX_VALUE)
                    .addComponent(jButton1)
                    .addGap(0, 167, Short.MAX_VALUE)))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(71, 71, 71)
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(129, Short.MAX_VALUE))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addGap(0, 135, Short.MAX_VALUE)
                    .addComponent(jButton1)
                    .addGap(0, 136, Short.MAX_VALUE)))
        );

        pack();
    }// </editor-fold>                        

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        cv.setToolTipText("ciao");
    }                                        

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new NewJFrame1().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                   
}