Strange result using transactions

I am executing the following queries (id has a unique key):

1) begin;
1) delete from forum where id = 20;
1) insert into forum (id, name) values (20, 'test');
2) delete from forum where id = 20;
1) commit;

Queries marked with 1) are executed by process 1 and queries marked with 2) 
are executed by process 2.

The problem is that process 2 gets the message 'DELETE 0'. I would expect 
him to get the message 'DELETE 1'.

Can anyone explain this behaviour?

Thanks in advance!

Matthijs Melissen