pg_advisory_lock is not waiting for unlock

To reproduce:

SELECT pg_advisory_lock(123);

-- Now a new lock appear in pg_locks
SELECT * FROM pg_locks WHERE locktype = 'advisory' AND objid = 123;

SELECT pg_advisory_lock(123); -- IS NOT WAITING, just a new lock in the pg_locks appear

-- to clear, pg_locks, pg_advisory_unlock must be called twice (it's not the right behavior...)
SELECT pg_advisory_unlock(123);

SELECT * FROM pg_locks WHERE locktype = 'advisory' AND objid = 123; -- still presente

SELECT pg_advisory_unlock(123);

SELECT * FROM pg_locks WHERE locktype = 'advisory' AND objid = 123; -- now empty