ADDITIONAL SYSTEM INFORMATION :
openjdk version "15.0.2" 2021-01-19
OpenJDK Runtime Environment (build 15.0.2+7-27)
OpenJDK 64-Bit Server VM (build 15.0.2+7-27, mixed mode, sharing)

Macbook Pro (13-inch, M1, 2020)

Big Sur
Version 11.2

A DESCRIPTION OF THE PROBLEM :
On a macbook pro, M1. When using the two finger gesture to scroll, occasionally the shift key will be reported as down.

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Simply run the MouseWheelEventDemo as modified here-in and observe the 'modifiers' output.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The modifiers variable should never be non-zero.
ACTUAL -
Occasionally it is.

---------- BEGIN SOURCE ----------
package utilities;

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
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 * documentation and/or other materials provided with the distribution.
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 * from this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
* MouseWheelEventDemo.java
*/

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;

import javax.swing.*;

public class MouseWheelEventDemo extends JPanel
        implements MouseWheelListener {
    JTextArea textArea;
    JScrollPane scrollPane;
    static final String NEWLINE = System.getProperty("line.separator");
    
    public static void main(String[] args) {
        /* Use an appropriate Look and Feel */
        try {
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
            //UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
            UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
        } catch (UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        } catch (IllegalAccessException ex) {
            ex.printStackTrace();
        } catch (InstantiationException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        /* Turn off metal's use of bold fonts */
        UIManager.put("swing.boldMetal", Boolean.FALSE);
        
        //Schedule a job for the event dispatch thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
    
    /**
     * Create the GUI and show it. For thread safety,
     * this method should be invoked from the
     * event dispatch thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("MouseWheelEventDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        //Create and set up the content pane.
        JComponent newContentPane = new MouseWheelEventDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
    
    public MouseWheelEventDemo() {
        super(new BorderLayout());
        
        textArea = new JTextArea();
        textArea.setEditable(false);
        scrollPane = new JScrollPane(textArea);
        scrollPane.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setPreferredSize(new Dimension(400, 250));
        add(scrollPane, BorderLayout.CENTER);
        textArea.append("This text area displays information "
                + "about its mouse wheel events."
                + NEWLINE);
        
        //Register for mouse-wheel events on the text area.
        textArea.addMouseWheelListener(this);
        
        setPreferredSize(new Dimension(450, 350));
        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
    }
    
    //Append to the text area and make sure the new text is visible.
    void eventOutput(String eventDescription, MouseWheelEvent e) {
        textArea.append(e.getComponent().getClass().getName()
        + ": "
                + eventDescription);
        textArea.setCaretPosition(textArea.getDocument().getLength());
    }
    
    public void mouseWheelMoved(MouseWheelEvent e) {
        String message;
        int notches = e.getWheelRotation();

        if (notches < 0) {
            message = "Mouse wheel moved UP "
                    + -notches + " notch(es)" + NEWLINE;
        } else {
            message = "Mouse wheel moved DOWN "
                    + notches + " notch(es)" + NEWLINE;
        }
        if (e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL) {
            message += " Scroll type: WHEEL_UNIT_SCROLL" + NEWLINE;
            message += " Scroll amount: " + e.getScrollAmount()
            + " unit increments per notch" + NEWLINE;
            message += " Units to scroll: " + e.getUnitsToScroll()
            + " unit increments" + NEWLINE;
            message += " Vertical unit increment: "
                    + scrollPane.getVerticalScrollBar().getUnitIncrement(1)
                    + " pixels" + NEWLINE;
        } else { //scroll type == MouseWheelEvent.WHEEL_BLOCK_SCROLL
            message += " Scroll type: WHEEL_BLOCK_SCROLL" + NEWLINE;
            message += " Vertical block increment: "
                    + scrollPane.getVerticalScrollBar().getBlockIncrement(1)
                    + " pixels" + NEWLINE;
        }
        int modifiers = e.getModifiersEx();
        if (modifiers != 0) {
            String modifiersText = MouseWheelEvent.getModifiersExText(modifiers);
            message += " modifiers "+modifiers+" " +modifiersText + NEWLINE;
        }
        message += NEWLINE;
        eventOutput(message, e);
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
none i've found.

FREQUENCY : often