src/macosx/classes/sun/lwawt/LWWindowPeer.java

*** 801,810 ****
--- 801,814 ----
          if (targetPeer == null || !targetPeer.isEnabled()) {
              return;
          }
  
          Point lp = targetPeer.windowToLocal(x, y, this);
+         int signum = (int) Math.signum(preciseWheelRotation);
+         if (wheelRotation == 0 && signum * wheelRotation < 1) {
+            wheelRotation = signum;
+         }
          // TODO: fill "bdata" member of AWTEvent
          // TODO: screenX/screenY
          postEvent(new MouseWheelEvent(targetPeer.getTarget(),
                  MouseEvent.MOUSE_WHEEL,
                  when, modifiers,