This is a regression of issue RT-31104.

When the table has a multiple selection it shouldn't single select until the mouse is released. This is how the ListView appears to operate.

Below is a test class to reproduce with a ListView for comparison:

1. Multi select on the table and then click to drag the selection. It will single select first and then drag.

2. Try the same on the ListView...


*************************************** Test Class *******************************************
import java.util.List;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.control.SelectionMode;
import javafx.scene.control.TableCell;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.input.ClipboardContent;
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 DragAndDropTest extends Application {

    @Override public void start(Stage primaryStage) {
       
        TableView<String> table = new TableView<>();
        // add some rows
        for ( int i = 1; i <= 10; i++ ) {
            table.getItems().add("" +i);
        }
        
        // add some columns
        for ( int i = 0; i < 3; i++ ) {
            final TableColumn<String, String> column =
                  new TableColumn<>("Column " + i);
            column.setPrefWidth(100);
            column.setCellFactory(c -> new TableCell<String, String>() {
               @Override protected void updateItem(String item, boolean empty) {
                   super.updateItem(item, empty);
                   if ( empty || getTableRow() == null ) {
                       setText("");
                   } else {
                       setText("row " + getTableRow().getItem() );
                   }
               }
           }) ;
            
            table.getColumns().add( column );
        }
        
        table.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
        
        // setup simple DND of row data...
        table.setOnDragDetected(( MouseEvent event) -> {
           List<String> sel = table.getSelectionModel().getSelectedItems();
           if ( sel != null ) {
              Dragboard db = table.startDragAndDrop(TransferMode.COPY);
              ClipboardContent content = new ClipboardContent();
              content.putString( String.join(", ", sel) );
              db.setContent(content);
              event.consume();
           }
        });
        
        // a listview for comparison
        ListView<String> list = new ListView<>();
        for ( int i = 1; i <= 10; i++ ) {
           list.getItems().add(""+ i);
        }
        list.getSelectionModel().setSelectionMode(SelectionMode.MULTIPLE);
        list.setOnDragDetected(( MouseEvent event) -> {
           List<String> sel = list.getSelectionModel().getSelectedItems();
           if ( sel != null ) {
              Dragboard db = table.startDragAndDrop(TransferMode.COPY);
              ClipboardContent content = new ClipboardContent();
              content.putString( String.join(", ", sel) );
              db.setContent(content);
              event.consume();
           }
        });
        
        primaryStage.setScene(new Scene(new HBox(20, table, list), 550, 350));
        primaryStage.show();
    }

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

}