Awesome post to Wikihelp by Ping Jiang, Software Quality Assurance Engineer, Autodesk.
The short version:
basically when the old stairs upgrade to Revit 2013 and mix with new stairs in the project, we just need to simply uncheck the visibility of ‘above’Riser Lines and Riser Lines, then the representation for them will be almost exactly the same [as pre-2013] in all the views.
Read the complete and detailed guide at:
Stairs Representation During Upgrade – WikiHelp
Riser lines and Riser lines?