title: problem with validationsummary and view model implementing INotifyDataErrorInfo
body: <p>I guess my question is how the heck does validationsummary determine what its going to show?</p>
  <p>I have a view model implementing INotifyDataErrorInfo and some validation errors get shown in my validationsummary whereas others do not and I can't see what the difference is.</p>
  <p>Also, how can I get object level errors to show up? For object level errors, do I use null string.empty or something different?</p>
  <h1>update</h1>
  <p>The 2 properties that will not show up in the validationsummary are observablecollection.</p>
  <p>Still not solved.</p>