title: In c#, text box issue when using custom source
body: <p>In c#, i have text box with autocomplete source from listView. 
  When i am typing the key, the textbox populate the suggestion.
  When i am selecting any one of the suggested text from list its working fine.
  But when i am trying to move down in the populated list using key board(down arrow), the text box is text is replaced with first item in the list. i cant move to the second item in the list.</p>
  
  <pre><code>private void textbox1_TextChanged(object sender, EventArgs e)
  {
      if (textbox1.Text != "")
      {
          TreeNode treeNode = TreeNode;
          string text = textbox1.Text;
          Boolean isContain = false;
  
          foreach (TreeNode subNode in treeNode.Nodes)
          {
              if (subNode.Name.StartsWith(text))
              {
                  if (subNode.Name.StartsWith(text))
                      suggestStageName.Add(subNode.Name);
                  isContain = true;
                  if (subNode.Name.Equals(textbox1.Text))
                     do corresponding event
              }
          }
          if (isContain)
          {
              textbox1.AutoCompleteCustomSource = suggestStageName;
              textbox1.AutoCompleteMode = AutoCompleteMode.Suggest;                 
              textbox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
          }
      }
  }       
  </code></pre>