FULL PRODUCT VERSION :
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 10.0.14393]

A DESCRIPTION OF THE PROBLEM :
When using button bar with buttons with different lengths, the width of the bar is less than needed. Hides some of the buttons.



REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package sample.test.project.local;

import javafx.application.Application;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonBar;
import javafx.scene.control.Label;
import javafx.scene.control.Tooltip;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Region;
import javafx.stage.Stage;

public class JavaFXTestApplication extends Application {
    public JavaFXTestApplication() {
    }

    @Override public void start(Stage primaryStage) throws Exception {

        Scene scene = new Scene(getContentPane());

        primaryStage.setTitle("ButtonBar Test Program");
        primaryStage.setScene(scene);
        primaryStage.sizeToScene();
        primaryStage.setOnCloseRequest((e) -> System.exit(0));
        for (int n = 9; n < 11; n++) {
            Stage stage = new Stage();
            stage.setScene(new Scene(getContentPane1(n, stage)));
            stage.sizeToScene();
            stage.show();
        }
        primaryStage.show();
    }

    private BorderPane getContentPane() {
        return new BorderPane(new Label("ButtonBar has an issue"));
    }

    public Parent getContentPane1(int n, Stage stage) {
        // ButtonBar buttonBar = new ButtonBar() {
        // @Override protected double computePrefWidth(double height) {
        // resizeButtons();
        // double w = super.computePrefWidth(height);
        // System.out.println("computePrefWidth(" + w + ")");
        // return w;
        // }
        //
        // private void resizeButtons() {
        // final List<? extends Node> buttons =getButtons();
        //
        // // determine the widest button
        // double widest = -1;
        // for (Node button : buttons) {
        // if (ButtonBar.isButtonUniformSize(button)) {
        // widest = Math.max(button.prefWidth(-1), widest);
        // }
        // }
        //
        // // set the width of all buttons
        // for (Node button : buttons) {
        // if (ButtonBar.isButtonUniformSize(button)) {
        // sizeButton(button, widest);
        // }
        // }
        // }
        //
        // private void sizeButton(Node btn, double pref) {
        // if (btn instanceof Region) {
        // Region regionBtn = (Region) btn;
        //
        // regionBtn.setPrefWidth(pref);
        // }
        // }
        //
        // };
        //
        ButtonBar buttonBar = new ButtonBar();
        buttonBar.setButtonMinWidth(Region.USE_PREF_SIZE);

        for (int i = n; i >= 1; i--) {
            buttonBar.getButtons().add(createButton("ok", "OK", true, "" + i));
        }

        return buttonBar;
    }

    private Node createButton(String name, String toolTip, boolean enabled, String buttonText) {
        Button button = new Button();
        button.setId(name + "Button");
        button.setTooltip(new Tooltip(toolTip));
        if (buttonText != null) {
            button.setText(buttonText);
        }
        button.setDisable(!enabled);
        button.setMinWidth(Region.USE_PREF_SIZE);
        return button;
    }

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

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Calling resizeButtons() before calling computePrefWidth seems to solve the issue. See the commented code in the source.