Possible SET SESSION AUTHORIZATION bug

It doesn't currently seem possible to switch between different users using
SET SESSION AUTHORIZATION.  If I log in as the superuser and switch to
another user that works, but if I then switch to a second user in succession
I get permission denied when I try to select from a table that the user does
have access to.  Following is a cut and paste of two sessions showing what I
mean (with certain details masked out).

defender# psql db1-U pgsql
lcome to psql 7.4, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help on internal slash commands
       \g or terminate with semicolon to execute query
       \q to quit

paygw=# set search_path to poi,public;
SET
paygw=# set session authorization poi;
SET
paygw=> select * from get_accountsettings_by_username('poi');
 settletype | fraudchecks | mer_id | username | cgipass |    test_card     |
testcard_status | network | dupchecks | gatewaypass |  duptime  |
itemtypes_allowed | debug_log
------------+-------------+--------+----------+---------+------------------+
-----------------+---------+-----------+-------------+-----------+----------
---------+-----------
 AUTO       | OFF         | 9300   | poi      | XXXX| XXXXXXXXXX         |
vital   | OFF       |             | 1 seconds | 1                 | ON
(1 row)

paygw=> reset session authorization;
RESET
paygw=# set search_path to jdonline,public;
SET
paygw=# set session authorization jdonline;
SET
paygw=> select * from get_accountsettings_by_username('jdonline');
ERROR:  permission denied for relation account_settings
CONTEXT:  PL/pgSQL function "get_accountsettings_by_username" line 5 at
select into variables
paygw=> \q

-------------
psql db1 -U jdonline

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help on internal slash commands
       \g or terminate with semicolon to execute query
       \q to quit

paygw=> set search_path to jdonline,public;
SET
paygw=> select * from get_accountsettings_by_username('jdonline');
 settletype | fraudchecks | mer_id | username | cgipass |    test_card     |
testcard_status | network | dupchecks | gatewaypass | duptime  |
itemtypes_allowed | debug_log
------------+-------------+--------+----------+---------+------------------+
-----------------+---------+-----------+-------------+----------+-----------
--------+-----------
 AUTO       | OFF         | 0502   | jdonline | XXXXXX|XXXX           | fhms
| ON        |             | 3 months | 1                 | ON
(1 row)

paygw=>