title: DatePicker.SelectedDate not changing when Text is input
body: <p>When my users select a date via the Calander control within the DatePicker, the value gets correctly bound to the underlying object. BUT, if the user types the date within the DatePicker, then clicks a button, the text is not set to the SelectedDate property. </p>
  
  <p>The user has to remove the cursor from the TextBox within the DatePicker for the bound object to be updated.</p>
  
  <pre><code> &lt;toolkit:DatePicker Name="_dpField" Grid.Column="1" MinWidth="100"
                 ToolTip="{Binding Path=ToolTipText}"
                 TextInput="_dpField_TextInput"
                 SelectedDate="{Binding Path=Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/&gt;
  </code></pre>
  
  <p>HELP! how do i make sure that this typed value is used within the buttons event code?</p>
  
  <p>Thanks!</p>