function parameters : bug?

pg 8.0.3
This behaviour seems odd to me:

CREATE TABLE mytable ( inta INTEGER
);

CREATE OR REPLACE FUNCTION myfunction (inta integer) RETURNS integer 
AS 
$body$ 
begin insert into mytable(inta) values (inta); return(0);
end;
$body$
LANGUAGE 'plpgsql';

select myfunction(123);

ERROR:  syntax error at or near "$1" at character 22
QUERY:  insert into myTable( $1 ) values ( $2 )
CONTEXT:  PL/pgSQL function "myfunction" line 2 at SQL statement

The problem is with the line in my myfunction: insert into mytable(inta) values (inta);

The server doesn't like the field name being the same as the name of
the function parameter. I don't see why, as I can see no opportunity
for ambiguity.

Problem vanishes with a different function parameter name:

CREATE OR REPLACE FUNCTION myfunction (my_inta integer) RETURNS
integer 
AS $body$ begin insert into myTable(inta) values (my_inta); return(0);
end;
$body$
LANGUAGE 'plpgsql'


But, this means that if I change the design of my tables, I have to
possibly change my function headers rather than merely the code inside
them.

regards
Richard