Wrong index choosen?

I hall
I have a query in this form:

empdb=# explain analyze select * from v_past_connections where id_user = 26195 and login_time > '2004-07-21';
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
Index Scan using idx_user_logs_login_time on user_logs (cost=0.00..14.10 rows=1 width=28) (actual time=66.890..198.998 rows=5 loops=1)
Index Cond: (login_time > '2004-07-21 00:00:00+02'::timestamp with time zone)
Filter: (id_user = 26195)
Total runtime: 199.083 ms
(4 rows)

as you see the index on the time stamp column is used

The table have indexes on both columns:

empdb=# explain analyze select * from v_past_connections where login_time > '2004-07-21';
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------
Index Scan using idx_user_logs_login_time on user_logs (cost=0.00..12.90 rows=481 width=28) (actual time=7.338..661.300 rows=22477 loops=1)
Index Cond: (login_time > '2004-07-21 00:00:00+02'::timestamp with time zone)
Total runtime: 676.472 ms
(3 rows)

empdb=# explain analyze select * from v_past_connections where id_user = 26195;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
Index Scan using idx_user_user_logs on user_logs (cost=0.00..252.47 rows=320 width=28) (actual time=4.420..100.122 rows=221 loops=1)
Index Cond: (id_user = 26195)
Total runtime: 100.348 ms
(3 rows)

The rows filtered out with both condictions are two order of magnitude differents,
also the extimated rows are close to real numbers:

empdb=# select count(*) from v_past_connections where id_user = 26195;
count
-------
221
(1 row)

empdb=# select count(*) from v_past_connections where login_time > '2004-07-21';
count
-------
22441
(1 row)

why then the planner choose to do an index scan using the filter that retrieve a bigger ammount of rows ? A bug ?

Regards
Gaetano Mendola