Wrong results from Parallel Hash Full Join

I came across $subject and reduced the repro query as below.

create table a (i int);
create table b (i int);
insert into a values (1);
insert into b values (2);
update b set i = 2;

set min_parallel_table_scan_size to 0;
set parallel_tuple_cost to 0;
set parallel_setup_cost to 0;

# explain (costs off) select * from a full join b on a.i = b.i;
QUERY PLAN
------------------------------------------
Gather
Workers Planned: 2
-> Parallel Hash Full Join
Hash Cond: (a.i = b.i)
-> Parallel Seq Scan on a
-> Parallel Hash
-> Parallel Seq Scan on b
(7 rows)

# select * from a full join b on a.i = b.i;
i | i
---+---
1 |
(1 row)

Tuple (NULL, 2) is missing from the results.

Thanks
Richard