As of 8u20, calling printPage() from inside an AnimationTimer callback no longer works as it did prior to that. Attempting it results in the following exception:

Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: Key not associated with a running event loop: java.lang.Object@2b4b3670

Here is a sample program illustrating the issue:

public class PrintBugTest extends Application {
    @Override
    public void start(Stage primaryStage) {
        ComboBox<Printer> printerComboBox = new ComboBox<>();
        printerComboBox.getItems().addAll(Printer.getAllPrinters());
        printerComboBox.getSelectionModel().select(Printer.getDefaultPrinter());
        Button btn = new Button("Print");
        
        btn.setOnAction(e -> {
             new AnimationTimer() {
            @Override
                public void handle(long l) {
                    stop();
                    Node node = new Circle(100, 200, 200);
                    PrinterJob job = PrinterJob.createPrinterJob();
                    job.setPrinter(printerComboBox.getValue());
                    job.printPage(node);
                    job.endJob();
                }
            }.start();
            
        });
        VBox root = new VBox();
        root.setSpacing(20);
        root.setAlignment(Pos.CENTER);
        root.setPadding(new Insets(10,10,10,10));
        root.getChildren().addAll(new HBox(new Label("Select Printer: "), printerComboBox), btn);
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}