DragOver/DragDropped events are not received after putting custom data into dragboard on Mac. Sample to reproduce:

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.DataFormat;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    Pane group;

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

    private Parent getContent() {
        VBox list = new VBox(10);

        final Button btn = new Button("Button");

        list.getChildren().add(btn);

        btn.setOnDragDetected(new EventHandler<MouseEvent>() {

            @Override
            public void handle(MouseEvent t) {
                System.out.println("OnDragDetected");

                Dragboard db = btn.startDragAndDrop(TransferMode.COPY);
                System.out.println("Transfer modes: " + db.getTransferModes());
                ClipboardContent cont = new ClipboardContent();
                cont.put(new DataFormat("dndwithcontrols.custom.bytes"), new byte[] {1, 2, 3, 4});
                db.setContent(cont);
                t.consume();
            }
        });

        btn.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent t) {
                System.out.println("OnDragOver");
                t.acceptTransferModes(TransferMode.ANY);
            }
        });

        btn.setOnDragDropped(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent t) {
                System.out.println("OnDragDropped");
                t.setDropCompleted(true);
            }
        });


        return list;
    }

    public void start(Stage stage) {
        stage.setX(100);
        stage.setY(100);
        stage.setWidth(300);
        stage.setHeight(300);
        Scene scene = new Scene(group = new VBox());
        group.getChildren().add(getContent());
        group.getChildren().add(getContent());
        stage.setScene(scene);
        stage.show();

    }
}