This used to work in 8.2:
pei=# select castsource::regtype, casttarget::regtype, castcontext from pg_cast order by 1,2;
But int 8.3 it says:
ERROR: XX000: could not find pathkey item to sort
LOCATION: make_sort_from_pathkeys, createplan.c:2812
--
Peter Eisentraut
http://developer.postgresql.org/~petere/