The difference between 4k and 32k is most probably unrelated to the version, but your database maximum string setting
SQL> show parameter max_string_size
NAME TYPE VALUE
------------------------------------ ----------- ------------
max_string_size string EXTENDED
STANDARD = 4k, EXTENDED = 32k
That said, its still interesting that we don't come back with 3 in both cases. I think that's a bug.
Please log a bug with Support (it carries more weight coming from a customer than if I do it).
Here is some additional test cases you can add to it
SQL> declare
2 x varchar2(100);
3 BEGIN
4 FOR i IN (SELECT MAX(CAST('USD' AS CHAR(3))) OVER() c FROM Dual)
5 LOOP
6 x := i.c;
7 END LOOP;
8 END;
9 /
PL/SQL procedure successfully completed.
SQL>
SQL> declare
2 x varchar2(100);
3 BEGIN
4 FOR i IN (SELECT *
5 FROM (SELECT MAX(CAST('USD' AS CHAR(3))) OVER() c
6 FROM Dual))
7 LOOP
8 x := i.c;
9 END LOOP;
10 END;
11 /
declare
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 8
ORA-06512: at line 8
SQL>
SQL> declare
2 x clob;
3 BEGIN
4 FOR i IN (SELECT *
5 FROM (SELECT MAX(CAST('USD' AS CHAR(3))) OVER() c
6 FROM Dual))
7 LOOP
8 select dump(i.c) into x from dual;
9 END LOOP;
10 dbms_output.put_line(x);
11 END;
12 /
Typ=96 Len=32767:
85,83,68,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,3
2,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,3
2,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
[snip]
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,3
2,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,3
2,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,
32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,3
2,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL> declare
2 x varchar2(100);
3 BEGIN
4 SELECT *
5 into x
6 FROM (SELECT MAX(CAST('USD' AS CHAR(3))) OVER() c
7 FROM Dual);
8 END;
9 /
declare
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 4
SQL>
SQL>
SQL>