Since db.collection.find().addSpecial() is deprecated in 3.2, I don't know if this should be fixed or just noted in the 3.2 incompatibility page, but
the following doesn't work

db.products.find( { }, { item: 1, qty: 1, _id: 0 } )._addSpecial( "$orderby", { qty: -1 } )

whereas without the $ prefix in the $orderby works

db.products.find( { }, { item: 1, qty: 1, _id: 0 } )._addSpecial( "orderby", { qty: -1 } )