Multiple parameters with the same name for functions.

Hi,

As I was working on my code generator app, I noticed that one is able to 
create a function with multiple parameters with the same name. For example:

create or replace function func_test(id integer,id varchar, id 
timestamp) returns void as
$$
begin   raise notice '%',id;
end;
$$
language plpgsql;

Is this a known behavior or a bug?

Regards,
Gevik.