bug! in 7.1.3 (for recursion function)

Hi,
please run below recursion function in 7.1.3
-----------------------------------------------------------
drop function listTest(int4);
create function listTest(int4)
returns text
as 'declare
mtype alias for $1;
begin
if mtype=0 then
return ''0'';
else
return mtype||listTest(mtype-1);
end if;
end;'
language 'plpgsql';
select listTest(5);
--------------------------------------
response:

111110 (in 7.1.3, incorrenct!)

543210 (in 7.0.3, correct!)

Please tell me how to slove this problem if I don't want to go back to 7.0.3.

Thanks
Xiaoming

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