to reproduce:
1. run any app with combobox;
2. click on the combobox to open popup;
3. put two fingers and start moving; while moving two fingers put the third finger to the touchpad.

Glass detected outstanding Java exception at -[GlassTouches(hidden) sendJavaTouchEvent:]:src/com/sun/mat/ui/GlassTouches.m:333
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at javafx.scene.Scene$ScenePeerListener.scrollEvent(Scene.java:2354)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleScrollGestureEvent(GlassViewEventHandler.java:699)
at com.sun.glass.ui.View.handleScrollGestureEvent(Unknown Source)
at com.sun.glass.ui.View.notifyScrollGestureEvent(Unknown Source)
at com.sun.glass.ui.GestureSupport.handleScrollingEnd(Unknown Source)
at com.sun.glass.ui.GestureSupport$1.touchCountChanged(Unknown Source)
at com.sun.glass.ui.TouchInputSupport.notifyEndTouchEvent(Unknown Source)
at com.sun.glass.ui.mac.MacTouchInputSupport.notifyEndTouchEvent(Unknown Source)
at com.sun.glass.ui.mac.MacGestureSupport.notifyEndTouchEvent(Unknown Source)

public void start(Stage primaryStage) {
        
        
        StackPane root = new StackPane();
        
        ComboBox cb = new ComboBox();
        for (int i = 0; i < 10; i++) {
            cb.getItems().add("Item - " + i);
        }
        root.getChildren().add(cb);
        
        Scene scene = new Scene(root, 300, 250);
        
        primaryStage.setTitle(VersionInfo.getRuntimeVersion());
        primaryStage.setScene(scene);
        primaryStage.show();
    }