Program: 67600
Project: 67600
Buggy source:
private void updateBuffer(){
  if (bIsPainting) {
    return;
  }
  if (chart == null) {
    return;
  }
  if (isDisposedPreviewCanvas()) {
    return;
  }
  Rectangle re=preview.getClientArea();
  final Rectangle adjustedRe=new Rectangle(0,0,re.width,re.height);
  if (adjustedRe.width - 2 * X_OFFSET <= 0 || adjustedRe.height - 2 * Y_OFFSET <= 0) {
    if (buffer != null && !buffer.isDisposed()) {
      buffer.dispose();
      buffer=null;
    }
    return;
  }
  bIsPainting=true;
  Image oldBuffer=null;
  if (buffer == null) {
    buffer=new Image(Display.getDefault(),adjustedRe);
  }
 else {
    Rectangle ore=buffer.getBounds();
    oldBuffer=buffer;
    if (!adjustedRe.equals(ore)) {
      buffer=new Image(Display.getDefault(),adjustedRe);
    }
  }
  GC gc=new GC(buffer);
  gc.setBackground(Display.getDefault().getSystemColor(SWT.COLOR_LIST_BACKGROUND));
  gc.fillRectangle(buffer.getBounds());
  final Bounds bo=BoundsImpl.create(X_OFFSET,Y_OFFSET,adjustedRe.width - 2 * X_OFFSET,adjustedRe.height - 2 * Y_OFFSET);
  IDeviceRenderer deviceRenderer=null;
  try {
    deviceRenderer=ChartEngine.instance().getRenderer("String_Node_Str");
    deviceRenderer.setProperty(IDeviceRenderer.GRAPHICS_CONTEXT,gc);
    bo.scale(72d / deviceRenderer.getDisplayServer().getDpiResolution());
    final Generator gr=Generator.instance();
    gr.setHighContrast(Display.getCurrent().getHighContrast());
    RunTimeContext rtc=new RunTimeContext();
    rtc.setScriptingEnabled(false);
    rtc.setMessageLookup(new ChartBuilderMessageLookup(this.wizardContext.getUIServiceProvider()));
    rtc.setRightToLeft(wizardContext.isRtL());
    rtc.setRightToLeftText(wizardContext.isTextRtL());
    rtc.setResourceFinder(wizardContext.getResourceFinder());
    rtc.setExternalizer(wizardContext.getExternalizer());
    gcs=gr.build(deviceRenderer.getDisplayServer(),(Chart)chart,bo,null,rtc,isProcessorEnabled() ? wizardContext.getProcessor() : null);
    gr.render(deviceRenderer,gcs);
    ChartWizard.removeException(ChartWizard.PreviewPainter_ID);
  }
 catch (  Exception ex) {
    buffer=oldBuffer;
    ChartWizard.showException(ChartWizard.PreviewPainter_ID,ex.getLocalizedMessage());
  }
 finally {
    gc.dispose();
    if (deviceRenderer != null) {
      deviceRenderer.dispose();
    }
  }
  if (oldBuffer != null && oldBuffer != buffer) {
    oldBuffer.dispose();
  }
  bIsPainting=false;
}

Fixed version (ground truth):
private void updateBuffer(){
  if (bIsPainting) {
    return;
  }
  if (chart == null) {
    return;
  }
  if (isDisposedPreviewCanvas()) {
    return;
  }
  Rectangle re=preview.getClientArea();
  final Rectangle adjustedRe=new Rectangle(0,0,re.width,re.height);
  if (adjustedRe.width - 2 * X_OFFSET <= 0 || adjustedRe.height - 2 * Y_OFFSET <= 0) {
    if (buffer != null && !buffer.isDisposed()) {
      buffer.dispose();
      buffer=null;
    }
    return;
  }
  bIsPainting=true;
  Image oldBuffer=null;
  if (buffer == null) {
    buffer=new Image(Display.getDefault(),adjustedRe);
  }
 else {
    Rectangle ore=buffer.getBounds();
    oldBuffer=buffer;
    if (!adjustedRe.equals(ore)) {
      buffer=new Image(Display.getDefault(),adjustedRe);
    }
  }
  GC gc=new GC(buffer);
  gc.setBackground(Display.getDefault().getSystemColor(SWT.COLOR_LIST_BACKGROUND));
  gc.fillRectangle(buffer.getBounds());
  final Bounds bo=BoundsImpl.create(X_OFFSET,Y_OFFSET,adjustedRe.width - 2 * X_OFFSET,adjustedRe.height - 2 * Y_OFFSET);
  IDeviceRenderer deviceRenderer=null;
  try {
    deviceRenderer=ChartEngine.instance().getRenderer("String_Node_Str");
    deviceRenderer.setProperty(IDeviceRenderer.GRAPHICS_CONTEXT,gc);
    bo.scale(72d / deviceRenderer.getDisplayServer().getDpiResolution());
    final Generator gr=Generator.instance();
    if (Display.getCurrent().getHighContrast()) {
      Color color=Display.getDefault().getSystemColor(SWT.COLOR_LIST_BACKGROUND);
      ColorDefinition cd=ColorDefinitionImpl.create(color.getRed(),color.getGreen(),color.getBlue());
      gr.setDefaultBackground(cd);
    }
    RunTimeContext rtc=new RunTimeContext();
    rtc.setScriptingEnabled(false);
    rtc.setMessageLookup(new ChartBuilderMessageLookup(this.wizardContext.getUIServiceProvider()));
    rtc.setRightToLeft(wizardContext.isRtL());
    rtc.setRightToLeftText(wizardContext.isTextRtL());
    rtc.setResourceFinder(wizardContext.getResourceFinder());
    rtc.setExternalizer(wizardContext.getExternalizer());
    gcs=gr.build(deviceRenderer.getDisplayServer(),(Chart)chart,bo,null,rtc,isProcessorEnabled() ? wizardContext.getProcessor() : null);
    gr.render(deviceRenderer,gcs);
    ChartWizard.removeException(ChartWizard.PreviewPainter_ID);
  }
 catch (  Exception ex) {
    buffer=oldBuffer;
    ChartWizard.showException(ChartWizard.PreviewPainter_ID,ex.getLocalizedMessage());
  }
 finally {
    gc.dispose();
    if (deviceRenderer != null) {
      deviceRenderer.dispose();
    }
  }
  if (oldBuffer != null && oldBuffer != buffer) {
    oldBuffer.dispose();
  }
  bIsPainting=false;
}