SELECT failed on secondary index when table's columns are ALL primary key

--Create table, all columns are primary key.
CREATE TABLE IF NOT EXISTS T (
   PK1 VARCHAR not null,
   PK2 VARCHAR not null,
   CONSTRAINT PK PRIMARY KEY (PK1, PK2)
);

--Create secondary index
CREATE INDEX IDX_T ON T
(
   PK2, PK1
);

--Test data
UPSERT INTO T VALUES('100', '200');
UPSERT INTO T VALUES('101', '201');
UPSERT INTO T VALUES('102', '202');
UPSERT INTO T VALUES('103', '203');
UPSERT INTO T VALUES('104', '204');

--make sure data was created correctly.
SELECT * FROM T;

--success
SELECT PK1, PK2 FROM T WHERE PK1='102';

--no result with conditions(pk2[=,>,<,>=,<=]'202')
EXPLAIN
SELECT PK1, PK2 FROM T WHERE PK2 = '202';

--no result
SELECT * FROM IDX_T WHERE ':PK2'='202'

--success
EXPLAIN
SELECT /*+ NO_INDEX*/ PK1, PK2 FROM T WHERE PK2 = '202';

--cleanup
DROP TABLE IF EXISTS T;

CREATE TABLE IF NOT EXISTS T (
   PK1 VARCHAR not null,
   PK2 VARCHAR not null,
   KV  VARCHAR,
   CONSTRAINT PK PRIMARY KEY (PK1, PK2)
);

--Create secondary index
CREATE INDEX IDX_T ON T
(
   PK2, PK1
);