select function & search_path problem/bug?

hi,

i have a problem with selecting function :

db=# select auxilium.exists('arx.mods', 'r');exists
--------t
(1 row)

db=# select exists('arx.mods', 'r');
ERROR:  syntax error at or near "'arx.mods'" at character 15
db=# show search_path;       search_path
---------------------------auxilium, pg_catalog, arx
(1 row)

why i have to  give  namespace name, when i have it already in search_path
?

(its in pg 7.4.3 and 8.0)

thanks