question about age()

is there a bug in age()?

test=*# select *, age(birthday), age (current_date-1, birthday) from birthday ;
id | birthday | age | age
----+------------+---------+-------------------------
1 | 2010-08-29 | 3 years | 2 years 11 mons 30 days
(1 row)

Time: 0,322 ms
test=*# select * from birthday where age(birthday) != age (current_date-1, birthday);
id | birthday
----+----------
(0 rows)

'3 years' != '2 years 11 mons 30 days', but i got 0 rows, why?

I'm using 9.2.4.

Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknown)
Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°