possible minor EXPLAIN bug?

Hello

I thing so Agg node doesn't set width well:

postgres=# explain select a,b from twocol;                       QUERY PLAN
----------------------------------------------------------Seq Scan on twocol  (cost=0.00..31.40 rows=2140 width=8)
(1 row)

postgres=# explain select sum(a) from twocol group by b;                          QUERY PLAN
----------------------------------------------------------------HashAggregate  (cost=42.10..44.60 rows=200 width=8) --<
wrongshould be 4  ->  Seq Scan on twocol  (cost=0.00..31.40 rows=2140 width=8)
 
(2 rows)

Agg get width directly from outer plan, what could be wrong.

Regards
Pavel Stehule