title: TimePicker value not changing property after loading value
body: <p>I have a <code>TimePicker</code> control from <code>Windows Phone Toolkit</code> placed on my settings page:</p>
  
  <pre><code>&lt;toolkit:TimePicker x:Name="DayStartTimePicker" ValueStringFormat="{}{0:t}"&gt;&lt;/toolkit:TimePicker&gt;
  </code></pre>
  
  <p>It works fine until I want to load a previously saved value to it</p>
  
  <pre><code>DayStartTimePicker.Value = SomeDateTimeValue;
  </code></pre>
  
  <p>After this, I can tap on the control and choose the time, but after confirming it the field's value remains unchanged (it has the <code>SomeDateTime</code> time, but not the one I selected).</p>
  
  <p>I guess I'm missing something, but I couldn't find anything on the internet to fix that issue.</p>