misleading error message in 8.5, and bad (?) way deferred uniqueness works

While testing deferred unique constraints I found this:

# CREATE TABLE test (
i INT4 PRIMARY KEY
);
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

# set constraints test_pkey deferred;
ERROR: constraint "test_pkey" does not exist

The constraint definitely exists:

# select * from pg_constraint where conname = 'test_pkey';
-[ RECORD 1 ]-+----------
conname | test_pkey
connamespace | 2200
contype | p
condeferrable | f
condeferred | f
conrelid | 17533
contypid | 0
conindid | 17536
confrelid | 0
confupdtype |
confdeltype |
confmatchtype |
conislocal | t
coninhcount | 0
conkey | {1}
confkey | [null]
conpfeqop | [null]
conppeqop | [null]
conffeqop | [null]
conbin | [null]
consrc | [null]

This (set ... deferred) works perfectly if i define the table like this:

# CREATE TABLE test (
i INT4 PRIMARY KEY DEFERRABLE INITIALLY IMMEDIATE
);
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

# set constraints test_pkey deferred;
SET CONSTRAINTS

Also.

As I understand (I might be wrong, so please clarify if I am), when I
create table with primary key that is "deferrable initially immediate",
it will act as immediate unless i will set it to deferred with "set
constraints".

If that's true, then why it works:
# INSERT INTO test (i) values (1), (2), (3);
INSERT 0 3
# update test set i = i + 1;
UPDATE 3

shouldn't it raise exception? and work *only* if i set the constraint to
deferred?

depesz

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