Charindex & Patindex: does not handle nvarchar(max) or varchar(max) correctly generates error msg 8152 when used on expression 1 by DB007

BOL States:
CHARINDEX ( expression1 ,expression2 [ , start_location ] )
If either expression1 or expression2 is of a Unicode data type (nvarchar or nchar) and the other is not, the other is converted to a Unicode data type. CHARINDEX cannot be used with text, ntext, and image data types.
--> So what about nvarchar(max) or varchar(max) as the input on: expression 1 & 2 ??

We have some odd behaviour between expression 1 & 2 on both charindex and patindex:
(They are not treated the same)

The following has been tested on SQL 2005 : SP3 (Affects both X32 & 64-bit editions)
Try the following:

-- The following will return error msg: 8152
-- Which is search for string ABCDEF (replicated 40000 times)
-- and try to find it in string : CDEF
-- Should return 0. And no error msg.
SELECT
    PATINDEX (
    (REPLICATE(CAST('ABCDEF' AS VARCHAR(MAX))
            ,40000))
            , 'CDEF')


-- The following will return results of 3
-- Try to find string: %CDEF% in string
-- ABCDEF (replicated 40000 times)
-- Should return 3. And no error msg.
SELECT
    PATINDEX ( '%CDEF%',
    (REPLICATE(CAST('ABCDEF' AS VARCHAR(MAX))
            ,40000))
    )
    
-- The following will return error msg: 8152
-- Which is search for string ABCDEF (replicated 40000 times)
-- and try to find it in string : CDEF
-- Should return 0. And no error msg.
SELECT
    CHARINDEX ( (REPLICATE(CAST('ABCDEF' AS VARCHAR(MAX))
            ,4000)),'CDEF'
    )
    
    
-- The following will return results of 3
-- Try to find string: %CDEF% in string
-- ABCDEF (replicated 40000 times)
-- Should return 3. And no error msg.
SELECT
    CHARINDEX ( 'CDEF',
    (REPLICATE(CAST('ABCDEF' AS VARCHAR(MAX))
            ,4000))
    )