Postgres Weird interval representation

weird_interval_output

postgres=# select '6 days 23:45:00'::interval - '6 days 23:23:00'::interval;
 ?column?
----------
 00:22:00
(1 row)

postgres=# select '00:46:00'::interval - '00:24:00'::interval;
 ?column?
----------
 00:22:00
(1 row)

postgres=# select '6 days 00:16:00'::interval - '5 days 23:54:00'::interval;
    ?column?
-----------------
 1 day -23:38:00
(1 row)

postgres=# select '5 days 23:47:00'::interval - '5 days 23:25:00'::interval;
 ?column?
----------
 00:22:00
(1 row)

postgres=# select '6 days 01:39:00'::interval - '6 days 01:18:00'::interval;
 ?column?
----------
 00:21:00
(1 row)