SortBy="LastPost" does not work

Hi:

  <CSBlog:WeblogList  runat="server" >

       <QueryOverrides SortBy="LastPost" SortOrder="Descending" />

I would have thought that I would see a list of blogs that were ordered by the date of the last post? But it doesn't work - the list of blogs seems to be in a random order. How do I order the blogs by last post date?

Thanks