Using queries containing pseudo-classes in JavaFX

I'm tring to use pseudo classes in programmtic query using Node.lookupAll() however this seems to give unexpected results.

I've searched online and can't find anything to suggest Node.lookupAll() wouldn't support psuedo classes...

public class Foo extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        PseudoClass pseudoClass = PseudoClass.getPseudoClass("custom");

        Label a = new Label();
        a.getStyleClass().add("foo");
        a.pseudoClassStateChanged(pseudoClass, false);

        Label b = new Label();
        b.getStyleClass().add("foo");
        b.pseudoClassStateChanged(pseudoClass, true);

        Label c = new Label();
        c.getStyleClass().add("foo");
        c.pseudoClassStateChanged(pseudoClass, true);


        HBox box = new HBox(a, b, c);
        primaryStage.setScene(new Scene(box));

        System.out.println(box.lookupAll(":custom").size()); // expected 2
        System.out.println(box.lookupAll(".foo:custom").size()); // expected 2
        System.out.println(box.lookupAll(".foo").size()); // expected 3, got 3
        System.out.println(box.lookupAll(":magichorse").size()); // expected 0 !!

    }

}

Output

4
3
3
4