package bugsverifying;

import javafx.application.Application;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application{
       public static void main(String[] args) {
        launch(Main.class, args);
    }

    private Parent getContent() {

        VBox list=new VBox();
        TextField box= new TextField("Hello world!!!");
        box.setPrefColumnCount(5);
        list.getChildren().addAll(box);
        return list;
    }

    public void start(Stage stage) {
        stage.setX(100);
        stage.setY(100);
        Scene scene = new Scene(getContent());
        stage.setScene(scene);
        stage.show();
    }
}

Also see http://javafx-jira.kenai.com/browse/RT-12979

And also, please, write in documentation in which circumstances pref columns count is taken into account.