SplitUpdate set wrong target list reference

[kainwen]

Bug Report

Greenplum version or build

6X (top commit 0eb8cd4a74adf0b10ceac334036f90bfeaa92faa), regerssion problem, regression commit is ebc448703a0b186fa25177fb48a7e5c5463270d7.

Step to reproduce the behavior

gpadmin@zlyu-rr:~/workspace/gpdb$ psql
psql (9.4.26)
Type "help" for help.

gpadmin=# drop table if exists test_update;
create table test_update(
"a"  varchar,
"b"  varchar,
"c"  varchar
) distributed by (b);

insert into test_update(a, b, c) values('3', '3', '2');
insert into test_update(a, b, c) values('3', '3', '2');

explain
UPDATE test_update
SET a = '3',
b = '3',
c = '2'
WHERE b = '3';

DROP TABLE
CREATE TABLE
INSERT 0 1
INSERT 0 1
                                       QUERY PLAN
-----------------------------------------------------------------------------------------
 Update on test_update  (cost=0.00..1.03 rows=1 width=12)
   ->  Redistribute Motion 1:2  (slice1; segments: 1)  (cost=0.00..1.03 rows=2 width=12)
         Hash Key: a
         ->  Split  (cost=0.00..1.03 rows=1 width=12)
               ->  Seq Scan on test_update  (cost=0.00..1.01 rows=1 width=12)
                     Filter: ((b)::text = '3'::text)
 Optimizer: Postgres query optimizer
(7 rows)

gpadmin=# UPDATE test_update
SET a = '3',
b = '3',
c = '2'
WHERE b = '3';
ERROR:  distribution key of the tuple (0, 1) doesn't belong to current segment (actually from seg1) (nodeModifyTable.c:716)  (seg0 127.0.1.1:6002 pid=213847) (nodeModifyTable.c:716)