title: List Items are not clearing
body: <p>I have a form in which I am displaying another form:</p>
  
  <pre><code>if (headerText == "")
  {
      MhrtTemplateColumn objMhrtTemplateColumn = 
              new MhrtTemplateColumn("", lstUnusedChannelTags);
      objMhrtTemplateColumn.ShowDialog();
  }
  else
  {
      MhrtTemplateColumn objMhrtTemplateColumn = 
              new MhrtTemplateColumn(ChannelDesc, lstUnusedChannelTags, CurrentTag);
      objMhrtTemplateColumn.ShowDialog();
  }
  </code></pre>
  
  <p>These are the overloaded constructors:</p>
  
  <pre><code>public MhrtTemplateColumn(string channelDescription, List&lt;string&gt; channelTags)
  {
      InitializeComponent();
      this.ChannelDescription = channelDescription;
      this.ChannelTags = new List&lt;string&gt;();
      this.ChannelTags.Clear();            
      this.ChannelTags = channelTags;
  }
  public MhrtTemplateColumn(string channelDescription, List&lt;string&gt; channelTags, string CurrentChannelTag)
  {
      InitializeComponent();
      this.ChannelDescription = channelDescription;
      this.ChannelTags = new List&lt;string&gt;();
      this.ChannelTags.Clear();
      this.ChannelTags = channelTags;
      this.CurrentChannelTag = CurrentChannelTag;
  }
  </code></pre>
  
  <p>This is the Window_Loaded event for MhrtTemplateColumn:</p>
  
  <pre><code>private void Window_Loaded(object sender, RoutedEventArgs e)
  {
      txtChannelDescription.Text = ChannelDescription;
      if (CurrentChannelTag != null &amp;&amp; CurrentChannelTag != "")
      {
          if(ChannelTags.Contains(CurrentChannelTag) == false)
              ChannelTags.Add(CurrentChannelTag);
          cmbChannelTag.ItemsSource = null;
          cmbChannelTag.ItemsSource = ChannelTags;
          cmbChannelTag.SelectedValue = CurrentChannelTag;
      }
      else
      {
          cmbChannelTag.ItemsSource = null;
          cmbChannelTag.ItemsSource = ChannelTags;
          cmbChannelTag.SelectedIndex = 0;
      }           
  }
  </code></pre>
  
  <p>My problem is when the else block is executed, a new item gets added to the list. After closing the form and displaying it again with code in if block the list still has the new item added previously. Why?</p>