Problem with timezone query

gistfile1.sql

CREATE TEMP TABLE reservations (
   reservation_id serial
 , start_on timestamptz NOT NULL
 , time_zone text);    -- we don't need this

INSERT INTO reservations (start_on, time_zone) VALUES
  ('2014-04-11 00:00+10', 'Australia/Sydney')     -- start date 4/11, use midnight in Sydney
, ('2014-04-12 00:00+10', 'Australia/Sydney')     -- start date 4/12, use midnight in Sydney
, ('2014-04-11 00:00-07', 'America/Los_Angeles')  -- start date 4/11, use midnight in SF
, ('2014-04-12 00:00-07', 'America/Los_Angeles'); -- start date 4/12, use midnight in SF

-- Now pretend current wall time just turned 4/12 00:00 PDT (-07)
-- We expect to get the reservation starting on 4/12 in Sydney
-- where it is currently 4/12 5PM and the reservation starting
-- on 4/12 in SF where it is midnight on 4/12.
SELECT start_on, time_zone 
     , start_on::timestamp             AS local_ts
     , start_on AT TIME ZONE time_zone AS ts_at_tz
     , current_date::timestamptz       AS lower_bound
     , (current_date + 1)::timestamptz AS upper_bound
FROM   reservations
WHERE  start_on >= ('2014-04-12')::timestamptz
AND    start_on < ('2014-04-13')::timestamptz;

-- We only find the reservation starting on 4/12 in SF though because they
-- condition of the query excludes the Sydney reservation which had its
-- start_on shifted to 2014-04-11 14:00+00 even though that day is not
-- actually over yet.
-- This is why I switched to using tsrange because then the start_on is
-- an actual range and you can check for overlaps.