You need to add a clause here for the release upgrade. When we push code to a cluster you have to account for both versions being in flight. Luckily its awfully easy in this case:

    map_view(DbName, {DDocId, Rev}, ViewName, QueryArgs, DbOptions) ->
        {ok, DDoc} = ddoc_cache:open_doc(mem3:dbname(DbName), DDocId, Rev),
        map_view(DbName, DDoc, ViewName, QueryArgs, DbOptions);

    map_view(DbName, DDoc, ViewName, QueryArgs, DbOptions) ->
        % same as before