Timestamp field in privilege tables is not populated upon GRANT

create user u@localhost;

create table t (a int);

create procedure pr() begin end;

grant select on test.t to u@localhost;

grant insert (a) on test.t to u@localhost;

grant execute on procedure test.pr to u@localhost;

grant proxy on root@localhost to u@localhost;

select `Timestamp`, `Table_name`, `Table_priv` from mysql.tables_priv where `Db` = 'test';

select `Timestamp`, `Column_name`, `Column_priv` from mysql.columns_priv where `Db` = 'test';

select `Timestamp`, `Routine_name`, `Proc_priv` from mysql.procs_priv where `Db` = 'test';

select `Timestamp`, `Proxied_user` from mysql.proxies_priv where User = 'u';

drop user u@localhost;

drop procedure pr;

drop table t;

select `Timestamp`, `Table_name`, `Table_priv` from mysql.tables_priv where `Db` = 'test';

Timestamp	Table_name	Table_priv

0000-00-00 00:00:00	t	Select

select `Timestamp`, `Column_name`, `Column_priv` from mysql.columns_priv where `Db` = 'test';

Timestamp	Column_name	Column_priv

0000-00-00 00:00:00	a	Insert

select `Timestamp`, `Routine_name`, `Proc_priv` from mysql.procs_priv where `Db` = 'test';

Timestamp	Routine_name	Proc_priv

0000-00-00 00:00:00	pr	Execute

select `Timestamp`, `Proxied_user` from mysql.proxies_priv where User = 'u';

Timestamp	Proxied_user

0000-00-00 00:00:00	root