"<IDLE> in transaction" can't be killed with pg_cancel_backend(). Is it a bug?

Dear helpful postgres people;

I've got a database deadlock. The initiating process was "<IDLE> in
transaction" with PID 2219.
Use of pg_cancel_backend() returns true, but does not actually kill the
process.

When this happens I kill the PID at the Unix level, which feels sort of
stupid, like driving on the hood
of a car on the freeway without a safety harness.

Should I expect pg_cancel_backend() to work in a case like this? If not
does this sound like a reportable bug?

Also: is there a way I can get the value of $1 in the select for update
shown below?

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# select version();
PostgreSQL 8.3.4 on x86_64-pc-linux-gnu, compiled by GCC cc (GCC) 4.1.2
20061115 (prerelease) (Debian 4.1.1-21)

# select procpid,now()-query_start,usename,substr(current_query,0,1000)
from pg_stat_activity order by 2 desc;

procpid | ?column? | usename |
---------+-------------------------+------------+-------------------------------------------------------------------
32507 | 22:31:09.736599 | jira | <IDLE>
2219 | 04:01:59.139841 | production | <IDLE> in transaction
3428 | 03:58:06.149227 | production | select object,utf8
from user_objects where userid = $1 for update
6574 | 03:46:35.627382 | production | select object,utf8
from user_objects where userid = $1 for update
4456 | 02:41:33.680257 | production | <IDLE>
26217 | 02:26:49.609589 | production | select object,utf8
from user_objects where userid = $1 for update
29562 | 02:17:00.434927 | production | select object,utf8
from user_objects where userid = $1 for update
2123 | 00:28:04.877832 | production | select object,utf8
from user_objects where userid = $1 for update
....

=# SELECT l.locktype,c.relname,l.pid,l.mode,granted from pg_locks
l,pg_class c where l.relation=c.oid order by relname,granted;

locktype | relname | pid |
mode | granted
----------+-------------------------------------+-------+------------------+---------
relation | context_keyvals | 5841 |
RowExclusiveLock | t
relation | context_keyvals_ckey | 5841 |
RowExclusiveLock | t
relation | context_objects | 2219 |
RowShareLock | t
relation | context_objects_pkey | 2219 |
AccessShareLock | t
relation | contexts | 2549 |
AccessShareLock | t
relation | contexts | 5841 |
RowShareLock | t
relation | contexts_id_key | 5841 |
AccessShareLock | t
relation | contexts_pkey | 5841 |
AccessShareLock | t
relation | contexts_publication_date_idx | 5841 |
AccessShareLock | t
relation | contexts_site_key_ct_id_journal_key | 5841 |
AccessShareLock | t
relation | contexts_site_key_ct_type_idx | 5841 |
AccessShareLock | t
relation | pg_class | 3738 |
AccessShareLock | t
relation | pg_class_oid_index | 3738 |
AccessShareLock | t
relation | pg_class_relname_nsp_index | 3738 |
AccessShareLock | t
relation | pg_locks | 3738 |
AccessShareLock | t
relation | pg_toast_3794455612 | 10155 |
AccessShareLock | t
relation | pg_toast_3794455612_index | 10155 |
AccessShareLock | t
tuple | user_objects | 26217 |
ExclusiveLock | f
tuple | user_objects | 6574 |
ExclusiveLock | f
tuple | user_objects | 2123 |
ExclusiveLock | f
tuple | user_objects | 29562 |
ExclusiveLock | f
relation | user_objects | 2123 |
RowShareLock | t
relation | user_objects | 26217 |
RowShareLock | t
relation | user_objects | 10155 |
AccessShareLock | t
tuple | user_objects | 3428 |
ExclusiveLock | t
relation | user_objects | 3428 |
RowShareLock | t
relation | user_objects | 6574 |
RowShareLock | t
relation | user_objects | 2219 |
RowShareLock | t
relation | user_objects | 29562 |
RowShareLock | t
relation | user_objects_pkey | 6574 |
AccessShareLock | t
relation | user_objects_pkey | 2123 |
AccessShareLock | t
relation | user_objects_pkey | 26217 |
AccessShareLock | t
relation | user_objects_pkey | 3428 |
AccessShareLock | t
relation | user_objects_pkey | 29562 |
AccessShareLock | t
relation | user_objects_pkey | 2219 |
AccessShareLock | t
relation | user_objects_pkey | 10155 |
AccessShareLock | t

# SELECT locktype, mode, granted, schemaname, relname
FROM pg_locks
INNER JOIN pg_stat_user_tables
ON pg_locks.relation = pg_stat_user_tables.relid
WHERE pg_locks.pid='2219';

locktype | mode | granted | schemaname | relname
----------+--------------+---------+------------+-----------------
relation | RowShareLock | t | public | context_objects
relation | RowShareLock | t | public | user_objects

# select pg_cancel_backend(2219);
pg_cancel_backend
-------------------
t

# SELECT locktype, mode, granted, schemaname, relname
FROM pg_locks
INNER JOIN pg_stat_user_tables
ON pg_locks.relation = pg_stat_user_tables.relid
WHERE pg_locks.pid='2219';

locktype | mode | granted | schemaname | relname
----------+--------------+---------+------------+-----------------
relation | RowShareLock | t | public | context_objects
relation | RowShareLock | t | public | user_objects
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