To reproduce:

right click on the popup and when the context menu will appear click the header of the popup.
The context menu will remain.

Expected behavior is the same as with ESC - it should close.

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

        HBox root = new HBox();
        datePicker = new DatePicker();
        root.getChildren().addAll(datePicker);
        scene = new Scene(root, 300, 200);

        stage.setScene(scene);
        stage.setTitle(VersionInfo.getRuntimeVersion());
        stage.show();
    }