Test case:

Input:
Drag source - button "Source"; Drag target - button "Destination".
onDragDetected event puts a string to the clipboard and transferMode is COPY.
Target doesn't support any transfer modes.

Expected outcome:
Target would never receive "onDragDropped" event. Source would never receive "onDragDone" event.

Actual outcome:
Target hasn't received "onDragDropped" event.
But source have received "onDragDone" event.

To reproduce drag "Source" button to "Destination".

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class TestDND extends Application {

    @Override
    public void start(Stage stage) {

        //Set up source
        final Button source = new Button("Source");
        
        source.setOnDragDetected(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent t) {
                Dragboard db = source.startDragAndDrop(TransferMode.COPY);

                ClipboardContent content = new ClipboardContent();
                content.putString(source.getText());
                db.setContent(content);

                t.consume();
            }
        });

        source.setOnDragDone(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent t) {
                System.out.println("onDragDone");
            }
        });
        
        //Set up target
        final Button target = new Button("Destination");

        target.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent t) {
                System.out.println("Accepted mode = " + t.getAcceptedTransferMode());
                t.consume();
            }
        });

        target.setOnDragDropped(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent t) {
                System.out.println("onDragDroppped");
                boolean result = false;
                
                if (t.getGestureSource() != target &&
                        t.getDragboard().hasString()) {
                    System.out.println("Accepted string: " + t.getDragboard().getString());
                    result = true;
                }
                System.out.println("result = " + result);
                t.setDropCompleted(result);
                t.consume();
            }
        });

        HBox root = new HBox(10d);
        root.getChildren().addAll(source, target);
        Scene scene = new Scene(root, 300, 250);

        stage.setScene(scene);
        stage.setTitle(System.getProperty("java.runtime.version") + "; " + System.getProperty("javafx.runtime.version"));
        stage.show();
    }

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