Run the following code, which creates a TableView with one column and one empty row.

import javafx.application.Application;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class TableColWidthBug extends Application {
   
   // boilerplate to build table, add it to a stage, and show stage
   public static void main(String[] args) {
       launch(args);
   }
   @Override public void start(Stage primaryStage) {
       StackPane root = new StackPane();
       root.getChildren().add( buildTable() );
       primaryStage.setScene(new Scene(root, 650, 150));
       primaryStage.show();
   }

   private TableView buildTable() {

      // create table with a bunch of column and no rows...
      TableView<Integer> table = new TableView<>();
      TableColumn<Integer, Integer> column = new TableColumn<>("Column");
      table.getColumns().add( column );
      column.setPrefWidth( 150 );
      table.getItems().add(1); // try commenting out this line
         
      return table;
   }
}

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Note the line where the column's width is set to 150 px.

If you run the example on the Java 8.0 public release, the column's width is 150 px, as expected. If you comment out the line that adds the row to the table, this has no effect on the column's width.

But if you run the example on Java 8u20 b13, the column's width is much less that 150 px. It looks like it is being autosized to the width of the header text...? Also, if you comment out the line that adds the row to the table, the problem goes away and the column's width is 150 px as it should be.