Add these lines to HelloComboBox:

    @Override public void start(final Stage stage) {
        stage.setTitle("ComboBox");
        stage.addEventFilter(KeyEvent.KEY_PRESSED, new EventHandler() {
            public void handle(Event event) {
                stage.setX(100);
                stage.setY(100);
            }
        });
...

0) Run HelloComboBox
1) Drop down a list with the mouse
2) Press any key
3) The stage moves but the drop down list stays in the same place

I'm wondering if the drop down list is also hidden/shown properly when the outer stage it hidden/shown. Please check this as part of the fix