title: Editable Combo box loses selected value when the item source is changed
body: <p>I have a editable combo box that looses value if the item source is changed such that the current selected item is removed from item source.</p>
  
  <p>The code is a s follows,</p>
  
  <pre><code>&lt;ComboBox x:Name="TableNameCombo"
            MinWidth="100"
            IsEditable="True"
            ItemsSource="{Binding TableNames}"
            SelectionChanged="TableNameCombo_SelectionChanged"
            Text="{Binding TableName,
                   ValidatesOnDataErrors=True,
                   UpdateSourceTrigger=PropertyChanged}" /&gt;
  </code></pre>
  
  <p><strong>If i am in differnent view when the Item source is changed, the value is retained.
  The value is lost only if the itemsource is changed when the view with combobox is active.</strong></p>
  
  <p>Please help me with how to retain the combobox value even if it is not present in itemsource and the item source changes when the view comtaining combobox is active</p>
  
  <p>Note:</p>
  
  <p>1.By view i mean i have a tabbed panel and have diferent view in all
      tabs.</p>
  
  <p>2.I am not talking about any fall back value. I just want to
      retain whatever the selected value was, even if it is not present in
      combo box item source.</p>
  
  <p><strong>Let me clear up the question to very simple requirement,</strong>
  This is my screenshot from sample applicaiton,</p>
  
  <p><img src="https://i.stack.imgur.com/S7rag.jpg" alt="enter image description here"></p>
  
  <p>When the user enter an item in text box and clicks remove item button the item is removed from the collection which is itemSource for Combobox. But when i do that the item is not displayed in combobox.
  <img src="https://i.stack.imgur.com/ZGCPg.jpg" alt="enter image description here"></p>
  
  <p><strong>My requirement is to still retain the item in combobox even though it is not in the collection.</strong></p>