Clause accidentally pushed down ( Possible bug in Making Vars outer-join aware)

Hi,
sqlancer benchmark raised an issue with pushing down clauses in LEFT
JOINs. Example:

DROP TABLE IF EXISTS t1,t2,t3,t4 CASCADE;
CREATE TABLE t1 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t2 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t3 AS SELECT true AS x FROM generate_series(0,1) x;
CREATE TABLE t4 AS SELECT true AS x FROM generate_series(0,1) x;
ANALYZE;

EXPLAIN (ANALYZE, COSTS OFF)
SELECT ALL t1.x FROM t1, t2
LEFT OUTER JOIN t3
ON t3.x
LEFT OUTER JOIN t4
ON t3.x
WHERE t4.x ISNULL;

We should get zero tuples, right? But we have the explain:
Nested Loop (actual time=0.024..0.028 rows=4 loops=1)
...

REL_15_STABLE works correctly. As I remember, it could be induces by new
machinery, introduced by the 'Making Vars outer-join aware' patch.

Sorry for flood, if you are working on that issue.

--
regards,
Andrey Lepikhov
Postgres Professional