The following query

SELECT alias1.* FROM
t1 AS alias1 INNER JOIN t1 AS alias2
ON alias2.a = alias1.b
WHERE alias1.b IN (
SELECT a FROM t1, t2
)

on the test data returns a single row with join_cache_level>2, and 7 rows with join_cache_level<=2. The latter is the correct result.

bzr version-info
revision-id: <email address hidden>
date: 2012-01-02 20:06:36 -0800
build-date: 2012-01-05 23:33:41 +0400
revno: 3376
branch-nick: maria-5.3

Reproducible on 5.3.2 and 5.3.3 releases, current 5.3, 5.5.

EXPLAIN with join_cache_level=3 (wrong result)

id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY alias1 ALL NULL NULL NULL NULL 7 100.00
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 5 func 1 100.00
1 PRIMARY alias2 hash_index a #hash#a:a 5:5 test.t1.a 7 28.57 Using where; Using join buffer (flat, BNLH join)
2 MATERIALIZED t1 index a a 5 NULL 7 100.00 Using where; Using index
2 MATERIALIZED t2 ALL NULL NULL NULL NULL 7 100.00
Warnings:
Note 1003 select `test`.`alias1`.`a` AS `a`,`test`.`alias1`.`b` AS `b` from `test`.`t1` `alias1` semi join (`test`.`t1` join `test`.`t2`) join `test`.`t1` `alias2` where (`test`.`alias2`.`a` = `test`.`alias1`.`b`)
SELECT alias1.* FROM
t1 AS alias1 INNER JOIN t1 AS alias2
ON alias2.a = alias1.b
WHERE alias1.b IN (
SELECT a FROM t1, t2
)

EXPLAIN with join_cache_level=2 (correct result):

id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY alias1 ALL NULL NULL NULL NULL 7 100.00 Using where
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 5 func 1 100.00
1 PRIMARY alias2 ref a a 5 test.alias1.b 2 100.00 Using index
2 MATERIALIZED t1 index a a 5 NULL 7 100.00 Using index
2 MATERIALIZED t2 ALL NULL NULL NULL NULL 7 100.00
Warnings:
Note 1003 select `test`.`alias1`.`a` AS `a`,`test`.`alias1`.`b` AS `b` from `test`.`t1` `alias1` semi join (`test`.`t1` join `test`.`t2`) join `test`.`t1` `alias2` where (`test`.`alias2`.`a` = `test`.`alias1`.`b`)
SELECT alias1.* FROM
t1 AS alias1 INNER JOIN t1 AS alias2
ON alias2.a = alias1.b
WHERE alias1.b IN (
SELECT a FROM t1, t2
)

Minimal optimizer_switch: semijoin=on,materialization=on,join_cache_hashed=on
Full optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on

Test case:

SET optimizer_switch = 'semijoin=on,materialization=on,join_cache_hashed=on';
SET join_cache_level = 3;

CREATE TABLE t1 ( a INT, b INT, KEY(a) );
INSERT INTO t1 VALUES
(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7);

CREATE TABLE t2 ( c INT );
INSERT INTO t2 VALUES (1),(2),(3),(4),(5),(6),(7);

SELECT alias1.* FROM
t1 AS alias1 INNER JOIN t1 AS alias2
ON alias2.a = alias1.b
WHERE alias1.b IN (
SELECT a FROM t1, t2
);

Expected result:
a b
1 1
2 2
3 3
4 4
5 5
6 6
7 7

Result:
a b
7 7