private void MainTabChanged(object sender, SelectionChangedEventArgs e)
{
    int tabItem = ((sender as TabControl)).SelectedIndex;
    if (e.Source is TabControl) // This is a soultion of those problem.
    {
        switch (tabItem)
        {
            case 0:    // Chatting
                Debug.WriteLine("Tab: Chatting");
                if (MainChatList.Items.Count > 0)
                {
                    MainChatList.SelectedIndex = MainChatList.Items.Count - 1;
                    MainChatList.ScrollIntoView(MainChatList.Items[MainChatList.Items.Count - 1]);
                }
                break;
            case 1:    // Users
                Debug.WriteLine("Tab: Users");
                break;
            case 2:    // Friends
                Debug.WriteLine("Tab: Friends");
                this.OnFriendTabActive();
                break;
            default:
                Debug.WriteLine("Tab: " + tabItem);
                break;
        }
    }
}