Feature, my misconception or bug??

In PgSQL 7.4.12,

foodb=# SELECT '255.255.255.255/24'::cidr;
ERROR:  invalid cidr value: "255.255.255.255/24"
DETAIL:  Value has bits set to right of mask.
foodb=# 

SELECT '255.255.255.255/25'::cidr;       cidr
--------------------255.255.255.255/25
(1 row)

foodb=# 

in this case 
11111111.11111111.11111111.11111111 
has no bits set to right of                    8 LSB ^
??
-- 
-Achilleus