possible 7.1beta3 bug with union and order by a function

The query below used to work with 7.0.3. If I change 'lower(title)' to
'title' in the order by clause, then the query is accepted.

area=> select code, wbc.gameid, title from games, wbc where wbc.gameid = games.gameid union select code, null, null as title from wbc where gameid is null order by code, lower(title);
ERROR: Attribute 'title' not found