Question about conccurrency control and Insert

Hi

I currently use pgsql 7.2.4 (but the following has also been seen on
pgsql 7.3.3) with a transaction level set to "read committed".
It do a lot of little tests to understand how concurrency control works.
Let see this scenario:

We have a table named "test_count" and a field named "count"
The table contains 1 entry with count=1

Client 1:
BEGIN;
SELECT count FROM test_count FOR UPDATE; --> returns the only entry "1"
...

Client 2 :
BEGIN;
SELECT count FROM test_count FOR UPDATE; --> this query is blocked, ok
...

We continue :

Client 1:
INSERT INTO test_count VALUES (2);
COMMIT;

Client 2: (after commit of client 1)
[The select that was blocked is now free. But the result is the
first row containing "1". I'm surprised by this result]
SELECT count FROM test_count; --> now returns the two rows, on
containing "1", the other containing "2"
COMMIT;

So my question is : why the SELECT...FOR UPDATE of client 2, when
unblocked, returns only one row, and a following SELECT in the same
transaction returns two rows ? Is there a mechanisme I don't understand ?

Thanks for your response.