Fail of a return query from plpgsql function for a specific table

Hi all,I have a table accgroups and many others. I have written a test
function as follows.
CREATE OR REPLACE FUNCTION uf_testfunction()
RETURNS SETOF associates AS
$BODY$
begin
return query select * from associates;
return;
end;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
This works fine for above table but not works at all for accgroups table. As
I searched for this over web, it is identified as a bug for tables whose
columns are changed(deleted and added). Is it true?
How to solve this issue?
Thanks
CPK