Error in date_trunc function?

Compare TZ part of date_func function output with param 'month' and other.
Is it error?

netquote=> select date_trunc('century', now());
date_trunc
------------------------
2000-01-01 00:00:00+03
(1 row)

netquote=> select date_trunc('year', now());
date_trunc
------------------------
2001-01-01 00:00:00+03
(1 row)

netquote=> select date_trunc('month', now());
date_trunc
------------------------
2001-10-01 00:00:00+04
(1 row)

netquote=> select date_trunc('day', now());
date_trunc
------------------------
2001-10-31 00:00:00+03
(1 row)

netquote=> select date_trunc('hour', now());
date_trunc
------------------------
2001-10-31 18:00:00+03
(1 row)

netquote=> select date_trunc('minute', now());
date_trunc
------------------------
2001-10-31 18:12:00+03
(1 row)

netquote=> select date_trunc('second', now());
date_trunc
------------------------
2001-10-31 18:12:24+03
(1 row)

--
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