Wrong results of function age(timestamp, timestamp)

Hello,

I ecountered strange behaviour of function age(timestamp, timestamp).

Let's say we have two timestamps and we want to compute their age() from
fixed timestamp in past:

SELECT pg_catalog.age('2016-04-30 00:00:01'::TIMESTAMP , '2015-01-01
12:00:00'::TIMESTAMP),
pg_catalog.age('2016-04-29 23:59:59'::TIMESTAMP , '2015-01-01
12:00:00'::TIMESTAMP);

age | age
--------------------------------+--------------------------------
1 year 3 mons 28 days 12:00:01 | 1 year 3 mons 28 days 11:59:59

Results are correct.

If we add '1 day'::interval to original timestamps, both results should be 1
day longer.
Howewer first result is exactly 24 hours longer than it should be:

SELECT pg_catalog.age(('2016-04-30 00:00:01'::TIMESTAMP + '1
day'::INTERVAL), '2015-01-01 12:00:00'::TIMESTAMP),
pg_catalog.age(('2016-04-29 23:59:59'::TIMESTAMP + '1
day'::INTERVAL), '2015-01-01 12:00:00'::TIMESTAMP);
age | age
--------------------------------+--------------------------------
1 year 3 mons 30 days 12:00:01 | 1 year 3 mons 29 days 11:59:59

Am I missing something or is it a bug in function age(timestamp, timestamp)?

I tested this on postgres versions 9.4.6 and 9.5.3 on CentOS 7, using
timezone = 'Europe/Prague' in postgresql.conf.

Regards
Michal Merta

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