Nothing has changed in that regard. We've never shown cms content on the edit pages. You can make the columns take up their space but it won't render any side content from the cms page there. You already have AlwaysShowLeftColumn so that should be working but if you want the right one too then you need to add AlwaysShowRightColumn="true"
You didn't mention what version you upgraded from, but there have not been any changes related to this for a while.
Hope that helps,
Joe