FULL PRODUCT VERSION :
Picked up _JAVA_OPTIONS: -Djava.net.preferIPv4Stack=true
java version  " 1.7.0_21 " 
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

EXTRA RELEVANT SYSTEM CONFIGURATION :
Mouse/keyboard are Microsoft Wireless Multimedia. Standard Microsoft drivers.

A DESCRIPTION OF THE PROBLEM :
Using getModifiersEx() produces the wrong result in various situations when it is called from a mouse event.

When clicking right button it gives Button3 and the Meta key (which I am not pressing at the time) on the click and released events, but not on the pressed event.

When clicking any button with the Alt-Gr key it gives the button with Ctrl-Alt.

When the mouse is moved quickly the key pick-up seems a bit random.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the program (sorry it's a bit big, but it was generated by Netbeans). Try a few clicks in combination with the modifier buttons. Sample output (edited by hand with comments so you can see what actions generated the output) is:

Some annotated output follows. I can post the code (it uses Netbeans to generate it, so some tweaking may be needed) if it would help.


//left click
Button 1 pressed count=1
Button 1 released count=1
Button 1 clicked count=1

//Right-click
Button 3 pressed count=1
Button 3 released count=1 Meta
Button 3 clicked count=1 Meta

//alt-gr left click
Button 1 pressed count=1 Alt Ctrl
Button 1 released count=1 Alt Ctrl
Button 1 clicked count=1 Alt Ctrl

//Ctrl right click
Button 3 pressed count=1 Ctrl
Button 3 released count=1 Ctrl
Button 3 clicked count=1 Ctrl

//Right click again
Button 3 pressed count=1
Button 3 released count=1 Meta
Button 3 clicked count=1 Meta

//Shift right click
Button 3 pressed count=1
Button 3 released count=1 Shift
Button 3 clicked count=1 Shift

//alt right click
Button 3 pressed count=1 Alt
Button 3 released count=1 Alt
Button 3 clicked count=1 Alt

//quick movements
Button 1 pressed count=1
Button 1 released count=1 Ctrl
//note no click event at all

Button 1 pressed count=1
Button 1 released count=1 Ctrl
Button 1 clicked count=1 Ctrl

Button 1 pressed count=1
Button 1 released count=1 Alt
Button 1 clicked count=1 Alt

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Consistent and correct detection of which key(s) are pressed.
ACTUAL -
See  " Steps to reproduce "  above

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package testmouseclick;

import java.awt.event.MouseEvent;
import java.awt.event.InputEvent;

/**
 *
 * @author Peter_2
 */
public class MouseCLick extends javax.swing.JFrame {

  /**
   * Creates new form MouseCLick
   */
  public MouseCLick() {
    initComponents();
    jTA1.setText( " No of buttons:  " +java.awt.MouseInfo.getNumberOfButtons()+ " 
 " );
  }

  /**
   * 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() {

    jScrollPane2 = new javax.swing.JScrollPane();
    jTA1 = new javax.swing.JTextArea();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle( " Test Mouse Click " );

    jTA1.setColumns(20);
    jTA1.setRows(5);
    jTA1.addMouseListener(new java.awt.event.MouseAdapter() {
      public void mouseReleased(java.awt.event.MouseEvent evt) {
        jTA1MouseReleased(evt);
      }
      public void mouseClicked(java.awt.event.MouseEvent evt) {
        jTA1MouseClicked(evt);
      }
      public void mousePressed(java.awt.event.MouseEvent evt) {
        jTA1MousePressed(evt);
      }
    });
    jScrollPane2.setViewportView(jTA1);

    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(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, 390, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
      .addComponent(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, 300, Short.MAX_VALUE)
    );

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

  private void jTA1MouseClicked(java.awt.event.MouseEvent evt) {
    mouseAction(evt);
  }

  private void jTA1MousePressed(java.awt.event.MouseEvent evt) {
    mouseAction(evt);
  }

  private void jTA1MouseReleased(java.awt.event.MouseEvent evt) {
    mouseAction(evt);
  }

  private void mouseAction(java.awt.event.MouseEvent evt) {
    String s;
    int button, count, id, mask;
    button = evt.getButton();
    count = evt.getClickCount();
    mask=evt.getModifiersEx();
    id = evt.getID();

    switch (button) {
      case MouseEvent.BUTTON1:
        s =  " Button 1  " ;
        break;

      case MouseEvent.BUTTON2:
        s =  " Button 2  " ;
        break;

      case MouseEvent.BUTTON3:
        s =  " Button 3  " ;
        break;

      default:
        throw new AssertionError();
    }

    switch (id) {
      case MouseEvent.MOUSE_CLICKED:
        s +=  " clicked  " ;
        break;

      case MouseEvent.MOUSE_PRESSED:
        s +=  " pressed  " ;
        break;

      case MouseEvent.MOUSE_RELEASED:
        s +=  " released  " ;
        break;

      default:
        throw new AssertionError();
    }

    s +=  " count= "  + count;

    if ((mask & InputEvent.ALT_GRAPH_DOWN_MASK) !=0) {
      s+= "  Alt-Gr " ;
    }
    if ((mask & InputEvent.ALT_DOWN_MASK) !=0) {
      s+= "  Alt " ;
    }
    if ((mask & InputEvent.CTRL_DOWN_MASK) !=0) {
      s+= "  Ctrl " ;
    }
    if ((mask & InputEvent.META_DOWN_MASK) !=0) {
      s+= "  Meta " ;
    }
    if ((mask & InputEvent.SHIFT_DOWN_MASK) !=0) {
      s+= "  Shift " ;
    }
//    if ((mask & InputEvent.BUTTON1_DOWN_MASK) !=0) {
//      s+= "  Button1 " ;
//    }
//    if ((mask & InputEvent.BUTTON2_DOWN_MASK) !=0) {
//      s+= "  Button2 " ;
//    }
//    if ((mask & InputEvent.BUTTON3_DOWN_MASK) !=0) {
//      s+= "  Button3 " ;
//    }
    s+= " 
 " ;
    jTA1.append(s);

  }

  /**
   * @param args the command line arguments
   */
  public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate= " collapsed "  desc= "  Look and feel setting code (optional)  " >
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
     */
    try {
      for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
        if ( " Nimbus " .equals(info.getName())) {
          javax.swing.UIManager.setLookAndFeel(info.getClassName());
          break;
        }
      }
    } catch (ClassNotFoundException ex) {
      java.util.logging.Logger.getLogger(MouseCLick.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
      java.util.logging.Logger.getLogger(MouseCLick.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
      java.util.logging.Logger.getLogger(MouseCLick.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
      java.util.logging.Logger.getLogger(MouseCLick.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        new MouseCLick().setVisible(true);
      }
    });
  }
  // Variables declaration - do not modify
  private javax.swing.JScrollPane jScrollPane2;
  private javax.swing.JTextArea jTA1;
  // End of variables declaration
}

---------- END SOURCE ----------