Javafx BorderPane with 2 GridPanes, second GridPane not showing up

Question

I need two grids in a BorderPane which is placed in a tab. When I add them both everything seems fine, but on launch only the first grid is visible.

This is my code.

 public void start(Stage stage) throws Exception {
            BorderPane bp = new BorderPane();
            GridPane g1 = new GridPane();
            g1.add(new Button("b1"), 0, 0);
            GridPane g2 = new GridPane();
            g2.add(new Button("b2"), 0, 0);
            bp.setCenter(g1);
            bp.setBottom(g2);
            TabPane p = new TabPane();
            Tab tab = new Tab("Test tab");
            tab.setContent(bp);
            p.getTabs().add(tab);
            Scene s = new Scene(p);
            stage.setScene(s);
            stage.show();
        }

g2 is not showing up at all. What am I missing?