using of select (myfunction()).* is so slow

Hi all, im using a function of my own in a subquery, and when wonderig
about the slowliness of this one, y relalize that:

test=# SELECT (_xxfunction(854,'711H',11,false)).* ;
(4 filas)
--Result DELETED
Duración: 1069,465 ms


glyms=# SELECT * from _xxfunction(854,'711H',11,false) ;
(4 filas)
Duración: 228,699 ms

For privacy reasons, i just deleted the result and the function name,
but the resulst are obviously exactly the same, and the ().* form (which
i needed) is taking so much more...there is a reason why? A workaround?

Thanks!

Gerardo