BUG #6728: revoke grant cascade behaviour

The following bug has been logged on the website:

Bug reference: 6728
Logged by: daniel german
Email address: dmg(at)uvic(dot)ca
PostgreSQL version: 9.1.4
Operating system: Linux (Ubuntu)
Description:

Hi there,

I am trying to understand how postgresql implements REVOKE GRANT ...
CASCADE

First the scenario:

We have the default user, and five roles (a, b, m, x, y). user belongs to
all.

Consider the following code:

set session role none;
drop table sailors;
create table sailors (a int);
select * from user;
grant select on sailors to a with grant option;
grant select on sailors to b with grant option;
set session role b;
grant select on sailors to m with grant option;
set session role a;
grant select on sailors to m with grant option;
set session role none;
\dp
set session role m;
grant select on sailors to x;
grant select on sailors to y;
set session role none;
select * from information_schema.column_privileges where table_name =
'sailors' and column_name = 'a';
\dp
set session role a;
revoke select on sailors from m cascade;
set session role none;
select * from information_schema.column_privileges where table_name =
'sailors' and column_name = 'a';
\dp

What I am surprised is that m keeps the proviledge (via b) but x and y have
lost it. See below). is that the way it is supposed to be?

thank you for your time,

--daniel

temp=# select * from information_schema.column_privileges where table_name =
'sailors' and column_name = 'a';
grantor | grantee | table_catalog | table_schema | table_name | column_name
| privilege_type | is_grantable
---------+---------+---------------+--------------+------------+-------------+----------------+--------------
dmg | dmg | temp | public | sailors | a
| UPDATE | YES
dmg | dmg | temp | public | sailors | a
| SELECT | YES
dmg | dmg | temp | public | sailors | a
| REFERENCES | YES
dmg | dmg | temp | public | sailors | a
| INSERT | YES
dmg | a | temp | public | sailors | a
| SELECT | YES
dmg | b | temp | public | sailors | a
| SELECT | YES
b | m | temp | public | sailors | a
| SELECT | YES