planner's midjudge number of rows resulting, despite pretty obvious join

explain select ss, ARRAY(select id from foo where ss>0 and id between
7 and 156 order by random() limit 3) as v from
generate_series(1,1000000) ss;
QUERY PLAN
------------------------------------------------------------------------------------
Function Scan on generate_series ss (cost=0.00..9381.22 rows=1000 width=4)
SubPlan
-> Limit (cost=9.36..9.37 rows=3 width=8)
-> Sort (cost=9.36..9.74 rows=150 width=8)
Sort Key: (random())
-> Result (cost=0.00..7.42 rows=150 width=8)
One-Time Filter: ($0 > 0)
-> Seq Scan on foo (cost=0.00..7.05 rows=150 width=8)
Filter: ((id >= 7) AND (id <= 156))
(9 rows)

:(

no matter if I change last generate_series's range, it will always
estimate 1000 rows...

--
GJ