When instantiating a Label a Transparent Stage becomes opaque.
To reproduce:
1) Run the code below to see the correct behavior.
2) Uncomment the statement 'new Label()' and run the code. You will see the background become white and opacity to 1.



import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{

        primaryStage.initStyle(StageStyle.TRANSPARENT);
        StackPane root = new StackPane();
        Rectangle rectangle = new Rectangle(0, 0, 100, 100);
        root.getChildren().add(rectangle);
        primaryStage.setScene(new Scene(root, 300, 275, null));
        primaryStage.show();

        // uncomment line below and stage will be opacity 1
        //new Label();
    }


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