Found while looking at RT-19014 and RT-19578.

Take toys/HelloWorld/HelloMenu.

In line 192 add code (3 lines):

        ((VBox)scene.getRoot()).getChildren().add(menuBar);
        HBox hb = new HBox();
        hb.getChildren().addAll(new Button("Button"), new TextField("Some text"));
        ((VBox)scene.getRoot()).getChildren().addAll(hb);
        if (os != null && os.startsWith("Mac")) {

To reproduce issue, click on button, press F10 and press right. After that press left/right: it does two things: navigating in menu and moving caret in textField.