I think I would expect this behavior with how you have defined the constraints as the function results rather than just being strict comparisons to the timestamp field.
Instead of this-
Check constraints:
> "y2018_mis_ora_check" CHECK (date_part('year'::text, mis_ora) =
> 2018::double precision)
I would expect this-
Check constraints:
> "y2018_mis_ora_check" CHECK mis_ora) >= make_timestamp(2018, 1,
> 1, 0, 0, 0::double precision) AND < make_timestamp(2019, 1,
> 1, 0, 0, 0::double precision)