SQL*Loader REF columns

create type tsuns (
vards varchar2(20)
);
create type tsaimnieks (
vards varchar2(20),
suns ref tsuns
);
create table sunji of tsuns;
create table saimnieki of tsaimnieks;
insert into sunji tsuns('Reksis');

SQL*Loader control faila saturs:

load data
infile *
into table saimnieki
fields terminated by whitespace (
vards char,
suns ref(constant 'sunji', suns_),
suns_ filler char
)
begindata
Jānis Reksis

SQL*Loader Error: Invalid table specified as scope of a REF. Kāpēc?