BUG #18075: configuration variable idle_session_timeout not working as expected

The following bug has been logged on the website:

Bug reference: 18075
Logged by: Muhammad Ali Ansari
Email address: maliansari(dot)coder(at)gmail(dot)com
PostgreSQL version: 15.4
Operating system: ubuntu 22.04
Description:

I have set the idle_session_timeout variable as 60000 making it 60 seconds
as defined in documentation, I ran some queries in parallel and created
connections performed transactions and closed the connections, I checked the
connection count it was 27, from which 20 are the ones that were created
during execution of queries. The idle connections remain there even after 60
seconds timeout has passed. I am using following query to get the
connections and duration elapsed since state_change.

SELECT
datname,
pid,
query,
usename,
client_addr,
client_port,
state,
backend_xid,
EXTRACT(MINUTE FROM (current_timestamp - state_change)) as duration
FROM pg_stat_activity
WHERE
datname = 'postgres'
AND pid <> pg_backend_pid()
AND state = 'idle'
ORDER BY
backend_start DESC;

It gives following results:

datname | pid | query | usename | client_addr | client_port | state |
backend_xid | duration
----------+-----+--------+---------+-------------+-------------+-------+-------------+----------
postgres | 975 | COMMIT | apiuser | ::1 | 45748 | idle |
| 28
postgres | 974 | COMMIT | apiuser | ::1 | 45738 | idle |
| 28
postgres | 973 | COMMIT | apiuser | ::1 | 45724 | idle |
| 28
postgres | 972 | COMMIT | apiuser | ::1 | 45718 | idle |
| 28
postgres | 971 | COMMIT | apiuser | ::1 | 45714 | idle |
| 28
postgres | 970 | COMMIT | apiuser | ::1 | 45698 | idle |
| 28
postgres | 969 | COMMIT | apiuser | ::1 | 45696 | idle |
| 28
postgres | 968 | COMMIT | apiuser | ::1 | 45686 | idle |
| 28
postgres | 967 | COMMIT | apiuser | ::1 | 45670 | idle |
| 28
postgres | 966 | COMMIT | apiuser | ::1 | 45658 | idle |
| 28
postgres | 965 | COMMIT | apiuser | ::1 | 45648 | idle |
| 28
postgres | 964 | COMMIT | apiuser | ::1 | 45634 | idle |
| 28
postgres | 963 | COMMIT | apiuser | ::1 | 45620 | idle |
| 28
postgres | 962 | COMMIT | apiuser | ::1 | 45612 | idle |
| 28
postgres | 961 | COMMIT | apiuser | ::1 | 45608 | idle |
| 28
postgres | 960 | COMMIT | apiuser | ::1 | 45606 | idle |
| 28
postgres | 959 | COMMIT | apiuser | ::1 | 45592 | idle |
| 28
postgres | 958 | COMMIT | apiuser | ::1 | 45582 | idle |
| 28
postgres | 957 | COMMIT | apiuser | ::1 | 45574 | idle |
| 28
postgres | 956 | COMMIT | apiuser | ::1 | 45566 | idle |
| 28
(20 rows)

As we can see, it shows that the time is way more than 1 minute now it is 28
minutes and they are still idle and still open in postgres and not
disconnected as expected.

If I get the configuration from following query:
select name, setting
from pg_settings
where
name = 'idle_session_timeout'
OR name = 'idle_in_transaction_session_timeout';

it returns this:

name | setting
--------------------------------------------------+---------
idle_in_transaction_session_timeout | 60000
idle_session_timeout | 60000
(2 rows)