ADDITIONAL SYSTEM INFORMATION :
JDK 1.8 u112 -> u171, JDK 1.9, JDK 10.0.1
macOS High Sierra 10.13.4
Macbook Pro with Magic Mouse/built-in trackpad/external Mac Trackpad

A DESCRIPTION OF THE PROBLEM :
When scrolling on macOS High Sierra using a magic mouse or a trackpad, Java dispatches several MouseWheelEvent instances with the shift key modifier and a scroll value that is the negative of what is expected.

REGRESSION : Last worked in version 8u161

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Scroll in a Swing JPanel using a magic mouse or magic trackpad.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
- all modEx values are 0
- all scroll values should be consistent with the scroll direction
ACTUAL -
- often events have a modEx value of 64
- in this case, the scroll value is the negative of what is expected

---------- BEGIN SOURCE ----------
Execute the following code and scroll on the panel:

  public static void main(String[] args) throws InvocationTargetException, InterruptedException {
    EventQueue.invokeAndWait(() -> {
      JFrame frame = new JFrame();
      JPanel content = new JPanel();
      content.setPreferredSize(new Dimension(100,100));
      content.addMouseWheelListener(e -> System.out.println("modEx: " + e.getModifiersEx() + " val:" + e.getPreciseWheelRotation()) );
      frame.add(content);
      frame.pack();
      frame.setVisible(true);
    });
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
ignore MouseWheelEvent instances with the shift modifier

FREQUENCY : always