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) --< wrong should 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