title: Bind selected value on combobox to view model
body: <p>I have my silverlight app which pulls data into a datagrid from a view model. The vm is exposed via Mef. I also have a details grid which has comboboxes. The vm also contains the data to populate the combobox values. Upon first load, everything works fine and the selected items on te comboboxes are correct and I can select alternative values. However, if I sort my main data grid (allow sort=true) then I find the binding for selected value on the comboboxes dissapear. The combobox is still populated with data but nothing is selected. </p>
  
  <p>Has anyone come across this issue before?  I am unsure how to solve this one. </p>
  
  <p>Thanks </p>