To reproduce:
Drag "source" to the "target".
At source I use only putUrl() and expect the hasUrl() to return true. So it does,
but hasFiles() also returns true.

You may also notice that source never reciever onDragDone event.

import java.io.File;
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.input.*;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class BugDnD extends Application {

    @Override
    public void start(Stage primaryStage) {

        final Button source = new Button("Source");

        source.setOnDragDetected(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                System.out.println("onDragDetected");

                Dragboard db = source.startDragAndDrop(TransferMode.MOVE);

                ClipboardContent content = new ClipboardContent();
                content.putUrl("www.oracle.com");
                db.setContent(content);

                event.consume();
            }
        });

        source.setOnDragDone(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                System.out.println("onDragDone");
                
                System.out.println("event.getTransferMode() = " + event.getTransferMode());

                event.consume();
            }
        });

        final Button target = new Button("Target");
        target.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                //System.out.println("onDragOver");

                if (event.getGestureSource() != target
                        && event.getDragboard().hasUrl()) {
                    event.acceptTransferModes(TransferMode.MOVE);
                }

                event.consume();
            }
        });

        target.setOnDragDropped(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                System.out.println("onDragDropped");
                
                Dragboard db = event.getDragboard();
                boolean success = false;
                if (db.hasUrl()) {
                    System.out.println(db.getUrl());
                    success = true;
                }
                if (db.hasFiles()) {
                    for (File file : db.getFiles()) {
                        System.out.println("file = " + file);
                    }
                }
                event.setDropCompleted(success);

                event.consume();
            }
        });


        HBox root = new HBox(20d);
        root.getChildren().addAll(source, target);
        Scene scene = new Scene(root, 300, 250);

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

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