COPY .. FREEZE, (apparently) not working on 9.6

Hello,

While testing "COPY/ FREEZE" feature, I've found a weird issue, by which I
am unable to actually freeze the rows/tables when using psql 9.6. Or, at
least, so it looks when inspecting 'xmin'..

Here is the actual (failing) output from running a simple COPY/FREEZE
snippet against postgres 9.6.2 (x86_64) on CentOS:

# /usr/pgsql-9.6/bin/psql -U postgres -h localhost
postgres=# BEGIN;
BEGIN
postgres=# CREATE TABLE da (text text);
CREATE TABLE
postgres=# COPY da FROM STDIN WITH (DELIMITER ',', FREEZE);
sample
\.
COPY 1
postgres=# COMMIT;
COMMIT
postgres=# select xmin,xmax from da;
xmin | xmax
—----+------
1679 | 0
(1 row)

However, this same snipped when run against 9.3.16, actually works, and
reports the expected xmin=2 value:

# /usr/pgsql-9.3/bin/psql -U postgres -h localhost
postgres=# BEGIN;
BEGIN
postgres=# CREATE TABLE da (text text);
CREATE TABLE
postgres=# COPY da FROM STDIN WITH (DELIMITER ',', FREEZE);
sample
\.
COPY 1
postgres=# COMMIT;
COMMIT
postgres=# select xmin,xmax from da;
xmin | xmax
—----+------
2 | 0
(1 row)

Both databases are just fresh installed, have no other users/sessions
concurrently, and have the same (default/basic) configuration.

Also, quite a similar issue happens when issuing a "VACUUM FREEZE da" after
COPY (w/o freeze): on 9.3 rows are frozen (xmin=2), while on 9.6 it just
like if VACUUM FREEZE is simply ignored.. :?

Regards

Danilo Olivares