MasterPageManager scripting

What is the trick to append a .HTT master page via scripting?

  var ma = RoboHelp.project.MasterPageManager;

  if (ma.count <= 0)

  {

      var path = "d:\\My_Documents\\My Projects\\My Masterpage.htt";

      ma.newItem("My", "My.css", "my desc");  // does not create a new entry?

      ma.importItem( path, true );            // does also not create a new enty?

    }

I also found a sample script "Master Page Import.jsx" which is also not appending a new master page?