title: CheckComboBox ValueMemberPath doesn't work
body: <p>The code-behind model (<code>Integers</code> in the code below) doesn't get filled with selected items. Is it a bug or do I miss something?</p>
  
  <p>XAML:</p>
  
  <pre><code>&lt;Window x:Class="DevicesRepositoryEditor.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:toolKit="clr-namespace:Xceed.Wpf.Toolkit;assembly=Xceed.Wpf.Toolkit"
          DataContext="{Binding RelativeSource={RelativeSource Self}}"
          &gt;
      &lt;StackPanel&gt;
          &lt;toolKit:CheckComboBox x:Name="Ccb"
              Delimiter=","
              VerticalAlignment="Center"
              ItemsSource="{Binding Pool}"
              DisplayMemberPath="Appearance"
              ValueMemberPath="Numeric"
              SelectedItemsOverride="{Binding Integers}" /&gt;
          &lt;!-- ...
              some more irrelevant stuff
          ... --&gt;
      &lt;/StackPanel&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>public class Composite{
      public Composite(string str, int num){ Appearance = str; Numeric = num; }
      public string Appearance { get; set; }
      public int Numeric { get; set; }
  }
  
  public partial class MainWindow : Window {
      public ObservableCollection&lt;Composite&gt; Pool { get; set; }
      public ObservableCollection&lt;int&gt; Integers { get; set; }
  
      public MainWindow(){
          Pool = new ObservableCollection&lt;Composite&gt;{
              new Composite("one", 1),
              new Composite("two", 2),
              new Composite("three", 3),
              new Composite("four", 4),
          };
          Integers = new ObservableCollection&lt;int&gt;();
          InitializeComponent();
      }
  
      /* ...
          some more irrelevant stuff
      ... */
  }
  </code></pre>