JPopupMenu positioning

I have a button, which, when clicked, should show a popup menu alignd
with its lower right corner.

The issue is that the popup menu shows in a wrong place with the first
click on the button, and in the correct one on every subsequent click,
even when moving or resizing the window.

source to display the problem:
-snip-
public class NewJFrame extends javax.swing.JFrame {
   
   /** Creates new form NewJFrame */
   public NewJFrame() {
       initComponents();
   }
   
   private void initComponents() {

       jPopupMenu1 = new javax.swing.JPopupMenu();
       jMenuItem1 = new javax.swing.JMenuItem();
       jMenuItem2 = new javax.swing.JMenuItem();
       jButton1 = new javax.swing.JButton();

       jMenuItem1.setText("Item 1");
       jPopupMenu1.add(jMenuItem1);

       jMenuItem2.setText("Item 2");
       jPopupMenu1.add(jMenuItem2);
 
       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 layout = new
               javax.swing.GroupLayout(getContentPane());
       getContentPane().setLayout(layout);
       layout.setHorizontalGroup(
               layout.createParallelGroup(javax
               .swing.GroupLayout.Alignment.LEADING)
               .addGroup(javax.swing.GroupLayout.Alignment
               .TRAILING, layout.createSequentialGroup()
               .addContainerGap(206, Short.MAX_VALUE)
               .addComponent(jButton1)
               .addContainerGap())
       );
       layout.setVerticalGroup(
         
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
           .addGroup(layout.createSequentialGroup()
               .addContainerGap()
               .addComponent(jButton1)
               .addContainerGap(219, Short.MAX_VALUE))
       );

       pack();
   }

   private void jButton1ActionPerformed(java.awt.event.ActionEvent
           evt) {
       // show the popupmenu
       jPopupMenu1.show(jButton1, jButton1.getWidth() -
               jPopupMenu1.getWidth(),
               jButton1.getHeight());
   }
   
   /**
    * @param args the command line arguments
    */
   public static void main(String args[]) {
       java.awt.EventQueue.invokeLater(new Runnable() {
           public void run() {
               new NewJFrame().setVisible(true);
           }
       });
   }
   
   private javax.swing.JButton jButton1;
   private javax.swing.JMenuItem jMenuItem1;
   private javax.swing.JMenuItem jMenuItem2;
   private javax.swing.JPopupMenu jPopupMenu1;
}
-snip-

Any way to make it behave the way I want to (show up in the correct
place on the first try)? I have tried

JFrame.invalidate()
JFrame.validate()
JFrame.pack()

JPopupMenu.invalidate()
JPopupMenu.validate()
JPopupMenu.pack()

I also tried to set the popup menus on screen location directly, but
never found out how to get the correct point. This might be a possible
solution, to call jPopupMenu1.setLocation().

Thanks again.