No warnings or errors after same sequential revoke

Hello!
Why we have no warnings  or errors about that  we have no such grant after first revoke?
postgres=> grant select(i2) on table user1.t2 to user2;
GRANT
postgres=> revoke select(i2) on table user1.t2 from user2;

REVOKE

postgres=> revoke select(i2) on table user1.t2 from user2;

REVOKE

postgres=> revoke select(i2) on table user1.t2 from user2;

REVOKE

postgres=> revoke select(i2) on table user1.t2 from user2;

REVOKE

-- 
Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company