title: Why does BooleanToVisibilityConverter seem to return "Hidden" (not "Collapsed") when passed DependencyProperty.UnsetValue?
body: <p>I've made a simple viewer of XAML documents that use a number of our own value converters, as well as built in ones, of course. It is expected behavior that there are DependencyProperty.UnsetValue bindings present.</p>
  
  <p>I'm encountering a problem where the resulting view of my document acts like the built-in BooleanToVisibilityConverter is returning "Hidden" in that situation. I had expected it to act as if false was the value passed in. I was not even aware that "Hidden" was a possible result, and no such thing is mentioned in the <a href="http://msdn.microsoft.com/en-us/library/system.windows.controls.booleantovisibilityconverter.aspx" rel="nofollow">MS docs</a>.</p>
  
  <p>Since I don't want to be changing the documents themselves to suit, I'm not planning to make a converter of my own that behaves as I expect. Any ideas out there to get what I want here, or even confirmation that what I'm seeing makes sense?</p>