LP:664594 - Wrong subquery result with join_cache_level=6, even in .result files

mysql-test/r/subselect3.result shows:

explain select t21.* from t21,t22 where t21.a = t22.a and
t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY subselect2 ALL unique_key NULL NULL NULL 8 Using temporary; Using filesort
1 PRIMARY t21 ALL NULL NULL NULL NULL 26 Using where; Using join buffer
1 PRIMARY t22 ALL NULL NULL NULL NULL 26 Using where; Using join buffer
2 SUBQUERY t11 ALL NULL NULL NULL NULL 8 Using where
2 SUBQUERY t12 ALL NULL NULL NULL NULL 8 Using where; Using join buffer
select t21.* from t21,t22 where t21.a = t22.a and
t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
a b c
256 67 NULL

while
mysql-test/r/subselect3_jcl6.result shows:

explain select t21.* from t21,t22 where t21.a = t22.a and
t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY subselect2 ALL unique_key NULL NULL NULL 8 Using temporary; Using filesort
1 PRIMARY t21 ALL NULL NULL NULL NULL 26 Using where; Using join buffer
1 PRIMARY t22 ALL NULL NULL NULL NULL 26 Using where; Using join buffer
2 SUBQUERY t11 ALL NULL NULL NULL NULL 8 Using where
2 SUBQUERY t12 ALL NULL NULL NULL NULL 8 Using where; Using join buffer
select t21.* from t21,t22 where t21.a = t22.a and
t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
a b c
256 67 NULL
256 67 NULL

That is, the _jcl6 variant produces two records instead of one.