Insert in table with UNIQUE index

Hi All!

I have a table with unique index with 2 exactly the same rows.
How it can be possible?

CREATE TABLE _inforgchngr6716_test
(
_nodetref bytea NOT NULL,
_noderref bytea NOT NULL,
_messageno numeric(10,0)
)
WITH (
OIDS=FALSE
);
ALTER TABLE _inforgchngr6716_test
OWNER TO postgres;

-- Index: _inforg6716_bynodemsg_rn_test

-- DROP INDEX _inforg6716_bynodemsg_rn_test;

CREATE UNIQUE INDEX _inforg6716_bynodemsg_rn_test
ON _inforgchngr6716_test
USING btree
(_nodetref, _noderref, _messageno);