ERROR: AlterTableAddConstraint:

Hi:

I needed to put some data in to a table using \copy
The table should look like:

CREATE TABLE AA (t timestamp default current_timestamp
CHECK (t = current_timestamp));

but in order to be able to load in the data, I had to
create the table without the constraint first. Now
I want to add in the constraint. Here is my trouble:

test=# create table a (t timestamp);
CREATE
test=# alter table a add check (t = current_timestamp);
ALTER
test=# create table b (t timestamp);
CREATE
test=# insert into b values (current_timestamp+'1 day');
INSERT 21076 1
test=# insert into a values (current_timestamp+'1 day');
ERROR: ExecAppend: rejected due to CHECK constraint $1
test=# alter table b add check (t = current_timestamp);
ERROR: AlterTableAddConstraint: rejected due to CHECK constraint <unnamed>

I tried a few things with DEFERRABLE and INITIALLY DEFERRED
but I cannot get the syntax right. Is this possible, or do I
have to hack around in the system tables to do this?