Postgresql date_trunc with time zone shifts zone by 1 hr, PostgreSQL

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--PostgreSQL 9.6
--'\\' is a delimiter

set time zone 'Europe/Berlin';

select count(*), current_setting('TimeZone')
from   generate_series(current_timestamp - interval '12 months', current_timestamp + interval '12 months', interval '1 month') tstz
where  date_trunc('month', tstz) <> date_trunc('month', tstz at time zone current_setting('TimeZone')) at time zone current_setting('TimeZone');

set time zone '+10:00';

set time zone 'CET';

create or replace function incompatible_tz_settings()
  returns setof text
  language plpgsql
as $func$
declare
  cur cursor for select name from pg_timezone_names;
begin
  for rec IN cur loop
    declare
      r pg_timezone_names;
    begin
      r := rec;
      execute format('set time zone %L', (r).name);
      if exists(select 1
                from   generate_series(current_timestamp - interval '12 months', current_timestamp + interval '12 months', interval '1 month') tstz
                where  date_trunc('month', tstz) <> date_trunc('month', tstz at time zone (r).name) at time zone (r).name) then
        return next (r).name;
      end if;
    end;
  end loop;
end
$func$;

select incompatible_tz_settings();

select name
from   pg_timezone_names
intersect
select abbrev
from   pg_timezone_abbrevs;


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