title: Resource (.resx) data is not saved
body: <p>I can't get what's the problem. Please check my code's fragments. Each time when I add resource data, it clears last data and writes new records in .resx. 
  For example, Applications.resx has "MyApp1" key with "MyApp1Path" value. Next time if I add "MyApp2" key with "MyApp2Path" value, I notice that {"MyApp1", "MyApp1Path"} doesn't exist. </p>
  
  <pre><code>//Adding Application in Applications List
  ResourceHelper.AddResource("Applications", _appName, _appPath);
  </code></pre>
  
  <p>Here is ResourceHelper class:</p>
  
  <pre><code>public class ResourceHelper
  {
      public static void AddResource(string resxFileName, string name, string value)
      {
          using (var resx = new ResXResourceWriter(String.Format(@".\Resources\{0}.resx", resxFileName)))
          {
              resx.AddResource(name, value);
          }
      }
  }
  </code></pre>