Program: 71932
Project: 71932
Buggy source:
private void createCustomPreviewPart(Composite parent){
  Group group;
  if (!isFormStyle())   group=new Group(parent,SWT.NONE);
 else   group=FormWidgetFactory.getInstance().createGroup(parent,"String_Node_Str");
  group.setText(LABEL_PREVIEW_GROUP);
  if (pageAlignment == PAGE_ALIGN_HORIZONTAL) {
    group.setLayoutData(new GridData(GridData.FILL_BOTH));
    group.setLayout(new GridLayout(1,false));
  }
 else {
    group.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
    group.setLayout(new GridLayout(2,false));
  }
  FormWidgetFactory.getInstance().createLabel(group,isFormStyle()).setText(LABEL_PREVIEW_DATETIME);
  if (!isFormStyle())   previewTextBox=new Text(group,SWT.SINGLE | SWT.BORDER);
 else   previewTextBox=FormWidgetFactory.getInstance().createText(group,"String_Node_Str",SWT.SINGLE);
  previewTextBox.setText(defaultDateTime == null ? "String_Node_Str" : defaultDateTime);
  GridData data=new GridData(GridData.FILL_HORIZONTAL);
  if (pageAlignment == PAGE_ALIGN_HORIZONTAL) {
    data.horizontalIndent=10;
  }
  previewTextBox.setLayoutData(data);
  previewTextBox.addModifyListener(new ModifyListener(){
    public void modifyText(    ModifyEvent e){
      setDefaultPreviewText(previewTextBox.getText());
      if (hasLoaded) {
        updatePreview();
      }
      if (StringUtil.isBlank(previewTextBox.getText())) {
        guideLabel.setText("String_Node_Str");
      }
 else {
        guideLabel.setText(ENTER_DATE_TIME_GUIDE_TEXT);
      }
    }
  }
);
  if (pageAlignment == PAGE_ALIGN_VIRTICAL) {
    FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  }
  guideLabel=FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  guideLabel.setText("String_Node_Str");
  Font font=JFaceResources.getDialogFont();
  FontData fData=font.getFontData()[0];
  fData.setHeight(fData.getHeight() - 1);
  guideLabel.setFont(new Font(Display.getCurrent(),fData));
  data=new GridData(GridData.FILL_HORIZONTAL);
  data.horizontalIndent=10;
  guideLabel.setLayoutData(data);
  Label label=FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  label.setText(LABEL_PREVIEW_LABEL);
  label.setLayoutData(new GridData());
  cusPreviewLabel=FormWidgetFactory.getInstance().createLabel(group,SWT.CENTER | SWT.HORIZONTAL | SWT.VIRTUAL,isFormStyle());
  cusPreviewLabel.setText("String_Node_Str");
  data=new GridData(GridData.FILL_BOTH);
  data.horizontalSpan=1;
  cusPreviewLabel.setLayoutData(data);
}

Fixed version (ground truth):
private void createCustomPreviewPart(Composite parent){
  Group group;
  if (!isFormStyle())   group=new Group(parent,SWT.NONE);
 else   group=FormWidgetFactory.getInstance().createGroup(parent,"String_Node_Str");
  group.setText(LABEL_PREVIEW_GROUP);
  if (pageAlignment == PAGE_ALIGN_HORIZONTAL) {
    group.setLayoutData(new GridData(GridData.FILL_BOTH));
    group.setLayout(new GridLayout(1,false));
  }
 else {
    group.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
    group.setLayout(new GridLayout(2,false));
  }
  FormWidgetFactory.getInstance().createLabel(group,isFormStyle()).setText(LABEL_PREVIEW_DATETIME);
  if (!isFormStyle())   previewTextBox=new Text(group,SWT.SINGLE | SWT.BORDER);
 else   previewTextBox=FormWidgetFactory.getInstance().createText(group,"String_Node_Str",SWT.SINGLE);
  previewTextBox.setText(defaultDateTime == null ? "String_Node_Str" : defaultDateTime);
  GridData data=new GridData(GridData.FILL_HORIZONTAL);
  if (pageAlignment == PAGE_ALIGN_HORIZONTAL) {
    data.horizontalIndent=10;
  }
  previewTextBox.setLayoutData(data);
  previewTextBox.addModifyListener(new ModifyListener(){
    public void modifyText(    ModifyEvent e){
      setDefaultPreviewText(previewTextBox.getText());
      if (hasLoaded) {
        updatePreview();
      }
      if (StringUtil.isBlank(previewTextBox.getText())) {
        guideLabel.setText("String_Node_Str");
      }
 else {
        guideLabel.setText(ENTER_DATE_TIME_GUIDE_TEXT);
      }
    }
  }
);
  if (pageAlignment == PAGE_ALIGN_VIRTICAL) {
    FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  }
  guideLabel=FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  guideLabel.setText("String_Node_Str");
  Font font=JFaceResources.getDialogFont();
  FontData fData=font.getFontData()[0];
  fData.setHeight(fData.getHeight() - 1);
  guideLabel.setFont(FontManager.getFont(fData));
  data=new GridData(GridData.FILL_HORIZONTAL);
  data.horizontalIndent=10;
  guideLabel.setLayoutData(data);
  Label label=FormWidgetFactory.getInstance().createLabel(group,isFormStyle());
  label.setText(LABEL_PREVIEW_LABEL);
  label.setLayoutData(new GridData());
  cusPreviewLabel=FormWidgetFactory.getInstance().createLabel(group,SWT.CENTER | SWT.HORIZONTAL | SWT.VIRTUAL,isFormStyle());
  cusPreviewLabel.setText("String_Node_Str");
  data=new GridData(GridData.FILL_BOTH);
  data.horizontalSpan=1;
  cusPreviewLabel.setLayoutData(data);
}