Inconsistent results in timestamp/interval comparison

Hi all,

I run the “official” deb package postgresql-16 v. 16.2-1.pgdg120+2 on a
Debian Bookworm system, and observed a confusing behavior in a
calculation with time stamps and intervals.

To reproduce, consider the following trivial example:

<snip>
create table testtab (t1 timestamp without time zone);
insert into testtab values ('2022-02-27 11:46:33'), ('2022-03-11
23:39:17'), ('2022-03-21 17:49:02');
test=# select now(), t1, (now() - t1) >= '2 years'::interval, now() >=
(t1 + '2 years'::interval) from testtab;
now | t1 | ?column? |
?column?
-------------------------------+---------------------+----------+----------
2024-03-04 12:59:39.796969+01 | 2022-02-27 11:46:33 | t | t
2024-03-04 12:59:39.796969+01 | 2022-03-11 23:39:17 | t | f
2024-03-04 12:59:39.796969+01 | 2022-03-21 17:49:02 | f | f
(3 Zeilen)
</snip>

According to the documentation, Table 9.31, IMHO both comparisons should
produce the same results, as

timestamp - timestamp → interval
timestamp + interval → timestamp

i.e.

(now() - t1) >= '2 years'::interval # add t1 on both sides of the
comparison
now() >= (t1 + '2 years'::interval)

As only the second example is wrong for the 1st comparison method, this
might indicate some rounding and/or insufficient precision issue.

Or did I miss something here?

Thanks in advance,
Albrecht.