Program: 58270
Project: 58270
Buggy source:
@Override public Boolean call() throws Exception {
  LOG.log(Level.INFO,"String_Node_Str");
  FileObject fileObject=dataObject.getPrimaryFile();
  final String content;
  try {
    content=fileObject.asText();
    if (content.endsWith("String_Node_Str") || content.endsWith("String_Node_Str")) {
      LOG.log(Level.INFO,"String_Node_Str");
      return false;
    }
    LOG.log(Level.INFO,"String_Node_Str");
  }
 catch (  IOException ex) {
    Exceptions.printStackTrace(ex);
    return false;
  }
  EditorCookie cookie=null;
  try {
    cookie=(EditorCookie)DataObject.find(fileObject).getCookie(EditorCookie.class);
  }
 catch (  DataObjectNotFoundException ex) {
    Exceptions.printStackTrace(ex);
  }
  if (cookie != null && cookie.getOpenedPanes() != null) {
    LOG.log(Level.INFO,"String_Node_Str");
    InsertNewLineInEditorTask action=new InsertNewLineInEditorTask(fileObject,cookie,lineEnding);
    WindowManager.getDefault().invokeWhenUIReady(action);
  }
 else {
    LOG.log(Level.INFO,"String_Node_Str");
    FileLock lock=FileLock.NONE;
    LOG.log(Level.INFO,"String_Node_Str");
    if (!fileObject.isLocked()) {
      lock=fileObject.lock();
      try {
        LOG.log(Level.INFO,"String_Node_Str",lineEnding);
        final String newContent=content + lineEnding;
        BufferedOutputStream os=new BufferedOutputStream(fileObject.getOutputStream(lock));
        os.write(newContent.getBytes("String_Node_Str"));
        os.flush();
        os.close();
      }
 catch (      IOException ex) {
        Exceptions.printStackTrace(ex);
        return false;
      }
 finally {
        lock.releaseLock();
      }
    }
  }
  return true;
}

Fixed version (ground truth):
@Override public Boolean call() throws Exception {
  LOG.log(Level.INFO,"String_Node_Str");
  FileObject fileObject=dataObject.getPrimaryFile();
  final String content;
  try {
    content=fileObject.asText();
    if (content.endsWith("String_Node_Str") || content.endsWith("String_Node_Str")) {
      LOG.log(Level.INFO,"String_Node_Str");
      return false;
    }
    LOG.log(Level.INFO,"String_Node_Str");
  }
 catch (  IOException ex) {
    Exceptions.printStackTrace(ex);
    return false;
  }
  EditorCookie cookie=null;
  try {
    cookie=(EditorCookie)DataObject.find(fileObject).getCookie(EditorCookie.class);
  }
 catch (  DataObjectNotFoundException ex) {
    Exceptions.printStackTrace(ex);
  }
  if (cookie != null && cookie.getDocument() != null) {
    LOG.log(Level.INFO,"String_Node_Str");
    InsertNewLineInEditorTask action=new InsertNewLineInEditorTask(fileObject,cookie,lineEnding);
    WindowManager.getDefault().invokeWhenUIReady(action);
  }
 else {
    LOG.log(Level.INFO,"String_Node_Str");
    FileLock lock=FileLock.NONE;
    LOG.log(Level.INFO,"String_Node_Str");
    if (!fileObject.isLocked()) {
      lock=fileObject.lock();
      try {
        LOG.log(Level.INFO,"String_Node_Str",lineEnding);
        final String newContent=content + lineEnding;
        BufferedOutputStream os=new BufferedOutputStream(fileObject.getOutputStream(lock));
        os.write(newContent.getBytes("String_Node_Str"));
        os.flush();
        os.close();
      }
 catch (      IOException ex) {
        Exceptions.printStackTrace(ex);
        return false;
      }
 finally {
        lock.releaseLock();
      }
    }
  }
  return true;
}