XML 함수 사용하면 결과가 이상해서 올려봅니다. (버전 12C)

WITH
A_TBL AS (
SELECT 'A' CD FROM DUAL UNION ALL
SELECT 'E' CD FROM DUAL UNION ALL
SELECT 'C' CD FROM DUAL UNION ALL
SELECT 'B' CD FROM DUAL UNION ALL
SELECT 'D' CD FROM DUAL
),
B_TBL AS (
SELECT 'B' CD ,'BB' DT FROM DUAL UNION ALL
SELECT 'D' CD ,'DD' DT FROM DUAL UNION ALL
SELECT 'C' CD ,'BB' DT FROM DUAL
),
C_TMP AS (
    SELECT A.*
          ,( -- A.CD를 1 LEVEL 참조
            SELECT DT
              FROM B_TBL 
             WHERE CD = A.CD
               AND ROWNUM = 1
           ) AA
          ,( -- A.CD를 2 LEVEL 참조
            SELECT DT
              FROM (
                SELECT DT
                  FROM B_TBL 
                 WHERE CD = A.CD
                   AND ROWNUM = 1
                )
           ) BB
          ,(
           SELECT SUBSTR(XMLAGG(XMLELEMENT(A, LEVEL)
                  ORDER BY 1).EXTRACT('//text()') ,1)
             FROM DUAL
            CONNECT BY LEVEL <=3
           ) XAGG 
     FROM A_TBL A
)
SELECT *
  FROM C_TMP
ORDER BY 1

결과
CD  AA  BB  XAGG
A			123
B	BB	BB	123
C	BB	BB	123
D	DD	DD	123
E			123
----------------

SELECT *
  FROM C_TMP
 WHERE AA = 'BB'  -- 1 LEVEL 참조필드
ORDER BY 1

결과
CD  AA  BB  XAGG
B	BB	BB	123
C	BB	BB	123
----------------

SELECT *
  FROM C_TMP
 WHERE BB = 'BB'  -- 2 LEVEL 참조필드 조건 안먹힘
ORDER BY 1
결과
CD  AA  BB  XAGG
----------------

XML 함수  ,(
           SELECT SUBSTR(XMLAGG( ....
           ) XAGG 
를 빼고 하면 2 LEVEL 참조필드 조건 먹힘

SELECT *
  FROM C_TMP
 WHERE BB = 'BB'  -- 2 LEVEL 참조필드 조건 먹힘
ORDER BY 1

결과
CD  AA  BB
B	BB	BB
C	BB	BB