diff value retuns, debug mode and play mode

I have a postgresql function at the bottom , when i run at EMS POSTGRESQL
debug mode with F8 step by step. Its work great but when i use with play
button it returns null what is the different about debug mode and run
mode.

BEST REGARDS.

CREATE OR REPLACE FUNCTION "public"."allocatedamount" (varchar, integer)
RETURNS numeric AS
$body$
/* allocatedamount (varchar,integer)
raporlarda kullan?lmak ?zere belirli bir sold un nekadar?n?n allocate
edildi?ini bulmak i?in
$1: Varchar: Tablo ismi.(SOCIAL,ACCOMODATION,vs)
$2: Integer: Soldid.
*/
declare
res numeric(15,2);
_pida integer[4]; _pid integer;
_rec record;
begin
if $1 = 'REGISTRATION' then begin
_pid:=1;
for _rec in select personaldetails.id from personaldetails where
personaldetails.id=$2 or personaldetails.masterid=$2 loop
_pida[_pid]:=_rec.id;
_pid:=_pid+1;
end loop;

select into res sum(allocatedpayments.amount) from allocatedpayments
where allocatedpayments.tablename='REGISTRATION' and
allocatedpayments.tableid = ANY (_pida::integer[]);
res=888;
end;
ELSIF $1 = 'MASTER-REGISTRATION' then
select into res sum(allocatedpayments.amount) from allocatedpayments
where allocatedpayments.tablename='REGISTRATION' and
allocatedpayments.tableid=$2;

ELSIF $1 = 'ACC-REGISTRATION' then
select into res sum(allocatedpayments.amount) from allocatedpayments
where allocatedpayments.tablename='REGISTRATION' and
allocatedpayments.tableid=$2;

else
select into res sum(allocatedpayments.amount) from allocatedpayments
where allocatedpayments.tablename=$1 and allocatedpayments.tableid=$2;

end if;

if res is null then
res:=0;
end if;

return res;

end;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;