[HACKERS] 200 = 199 + 1?

I just came across this very peculiar behavior:

=# create table foo(id int primary key);
CREATE TABLE
=# insert into foo select generate_series(1, 1000000);
INSERT 0 1000000
=# set enable_hashjoin to false; set enable_mergejoin to false;
SET
SET
=# explain select * from foo where id in (select i from generate_series(1, 200) i limit 199);
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Nested Loop  (cost=4.90..1648.52 rows=199 width=4)
   ->  HashAggregate  (cost=4.48..6.47 rows=199 width=4)
         Group Key: i.i
         ->  Limit  (cost=0.00..1.99 rows=199 width=4)
               ->  Function Scan on generate_series i  (cost=0.00..10.00 rows=1000 width=4)
   ->  Index Only Scan using foo_pkey on foo  (cost=0.42..8.24 rows=1 width=4)
         Index Cond: (id = i.i)
(7 rows)

=# explain select * from foo where id in (select i from generate_series(1, 200) i limit 200);
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Nested Loop  (cost=4.93..1653.00 rows=500000 width=4)
   ->  HashAggregate  (cost=4.50..6.50 rows=200 width=4)
         Group Key: i.i
         ->  Limit  (cost=0.00..2.00 rows=200 width=4)
               ->  Function Scan on generate_series i  (cost=0.00..10.00 rows=1000 width=4)
   ->  Index Only Scan using foo_pkey on foo  (cost=0.42..8.22 rows=1 width=4)
         Index Cond: (id = i.i)
(7 rows)