Hi;
Thx @Agustin - that was exactly my problem. I have been following PRISM since its days as the composite application pattern and I had put together an app at that time. I must have been following an example because I was using an ItemsControl for the composite view that contained a DataGrid. When I changed this over to a contentControl all was fine. I don't remeber why I chose an ItemsControl (which is why I think I was following an example). I think originally I was percieving that the PRISM markup extensions only worked with ItemsControl markup and not [generally] witha ny control.
I have also come to the realization (because I ran into it also) that Grid row defintions with a height [for a row def] set to auto will also cause the content to take the space it requires and the [vertical] ScrollBar will not be activated, which I guess is in line with the auto defintion.
Peter