Planner not using column limit specified for one column for another column equal to first

Hello.

I have a query that performs very poor because there is a limit on join
column that is not applied to other columns:

select * from company this_ left outer join company_tag this_1_ on
this_.id=this_1_.company_id left outer join company_measures companymea2_ on
this_.id=companymea2_.company_id left outer join company_descr ces3_ on
this_.id=ces3_.company_id where this_1_.tag_id = 7 and this_.id>50000000
and this_1_.company_id>50000000
order by this_.id asc limit 1000;

(plan1.txt)
Total runtime: 7794.692 ms

At the same time if I apply the limit (>50000000) to other columns in query
itself it works like a charm:

select * from company this_ left outer join company_tag this_1_ on
this_.id=this_1_.company_id left outer join company_measures companymea2_ on
this_.id=companymea2_.company_id left outer join company_descr ces3_ on
this_.id=ces3_.company_id where this_1_.tag_id = 7 and this_.id>50000000
and this_1_.company_id>50000000
and companymea2_.company_id>50000000 and ces3_.company_id>50000000
order by this_.id asc limit 1000;

(plan2.txt)
Total runtime: 27.547 ms

I've thought and someone in this list've told me that this should be done
automatically. But I have pretty recent server:
PostgreSQL 8.4.2 on amd64-portbld-freebsd8.0, compiled by GCC cc (GCC) 4.2.1
20070719 [FreeBSD], 64-bit
and it still do not work

Do I misunderstand something or this feature don't work in such a query?

Best regards, Vitalii Tymchyshyn