Subtracting Two Intervals

In porting from 7.4.19 to 8.3.1 I have found the following:

7.4.19:
mwr=# select interval '1 day 15 hours 30 minutes' - interval '29 hours';
?column?
--------------------
@ 10 hours 30 mins
(1 row)

8.3.1:
mwr83=# select interval '1 day 15 hours 30 minutes' - interval '29 hours';
?column?
----------------------------
@ 1 day -13 hours -30 mins
(1 row)

Is that right? I mean if you take 1 day (24 hours) and add -13 hours and -30
minutes, you get 10 hours and 30 minutes, but is it supposed to display that
way?

TIA
--
Terry Lee Tucker
Turbo's IT Manager
Turbo, division of Ozburn-Hessey Logistics
2251 Jesse Jewell Pkwy NE
Gainesville, GA 30501
Tel: (336) 372-6812 Fax: (336) 372-6812 Cell: (336) 404-6987
terry(at)turbocorp(dot)com
www.turbocorp.com