Possible deadlock issue when one transaction waiting on other and vice versa? Should, ideally, postgres recognize blocking situation?

Hi,

I have create the following tables:
1. rnc table
CREATE TABLE act_rnc(rnc_id integer NOT NULL PRIMARY KEY, rnc_data BYTEA);
2. rncgen table
CREATE TABLE act_rncgen(rnc_id integer NOT NULL PRIMARY KEY, rncsubObj_Cnt
integer, rncgen_data BYTEA);
3. iuo table which has a foreign key reference to rnc table
CREATE TABLE act_iuo(iuo_id integer NOT NULL primary key, rnc_id integer NOT
NULL, iuo_data BYTEA, FOREIGN KEY(rnc_id) references act_rnc(rnc_id) on
delete cascade);

Now i open two transactions (separate session with psql). In the first
transaction I give the following sql sequence:
begin;
update act_rnc set rnc_data='rnc_data' where rnc_id=1;

The transaction will be open.

In a second transaction i give the following sql sequence:
begin;
insert into act_iuo values (1,1,'iuo_data');

--> now the second transaction is blocked. I work with PostgreSQL 9.0.

Some outputs:
select * from pg_locks;
locktype | database | relation | page | tuple | virtualxid |
transactionid | classid | objid | objsubid | virtualtransaction | pid
| mode | granted

---------------+----------+----------+------+-------+------------+---------------+---------+-------+----------+--------------------+-------+------------------+---------

tuple | 16385 | 16427 | 0 | 8 |
| | | | | 3/80 | 9230 |
ShareLock | t

relation | 16385 | 10985 | | |
| | | | | 4/247 | 16535 |
AccessShareLock | t

virtualxid | | | | | 4/247
| | | | | 4/247 | 16535 |
ExclusiveLock | t

relation | 16385 | 16443 | | |
| | | | | 3/80 | 9230 |
RowExclusiveLock | t

transactionid | | | | | |
584 | | | | 3/80 | 9230 |
ExclusiveLock | t

virtualxid | | | | | 3/80
| | | | | 3/80 | 9230 |
ExclusiveLock | t

relation | 16385 | 16433 | | |
| | | | | 3/80 | 9230 |
AccessShareLock | t

relation | 16385 | 16427 | | |
| | | | | 5/535 | 2814 |
RowExclusiveLock | t

virtualxid | | | | | 5/535
| | | | | 5/535 | 2814 |
ExclusiveLock | t

transactionid | | | | | |
583 | | | | 5/535 | 2814 |
ExclusiveLock | t

relation | 16385 | 16449 | | |
| | | | | 3/80 | 9230 |
RowExclusiveLock | t

relation | 16385 | 16427 | | |
| | | | | 3/80 | 9230 |
RowShareLock | t

transactionid | | | | | |
583 | | | | 3/80 | 9230 |
ShareLock | f

relation | 16385 | 16433 | | |
| | | | | 5/535 | 2814 |
RowExclusiveLock | t

(14 rows)

select relname, pg_class.oid from pg_class;
act_rnc_pkey | 16433
pg_inherits_parent_index | 2187
pg_inherits_relid_seqno_index | 2680
pg_toast_16435 | 16438
pg_trigger_oid_index | 2702
pg_toast_16435_index | 16440
act_rncgen | 16435
act_rncgen_pkey | 16441
pg_toast_16443 | 16446
pg_toast_16443_index | 16448
act_iuo_pkey | 16449
pg_amop | 2602
act_iuo | 16443
pg_largeobject | 2613
act_rnc | 16427
pg_toast_11361 | 11363
pg_toast_11361_index | 11365
pg_toast_11366_index | 11370

I assume that the access to act_rnc_pkey causes the blocking, however why?
Or how I can resolve the blocking (commit one transaction solves the
problem, but should Postgres not recognize the blocking situation and
release one transaction?). Is this an error in Postgres?

--
Cheers,
Prakash