CodeArea seems to intercept the input method, preventing it from being passed to other TextFields.

[impactCn]

demo

public class Undefined extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {
        CodeArea codeArea = new CodeArea();
        Button button = new Button("Button");
        TextField textField = new TextField();
        button.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {
                Popup popup = new Popup();
                popup.getContent().add(textField);
                popup.show(primaryStage);
            }
        });
        textField.setOnKeyPressed(new EventHandler<KeyEvent>() {
            @Override
            public void handle(KeyEvent keyEvent) {
                // debug
                System.err.println(keyEvent.getCode());
            }
        });
        VBox vBox = new VBox();
        vBox.getChildren().addAll(codeArea, button);
        Scene scene = new Scene(vBox, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

test