Query broken under 7.1RC2

This query worked under 7.0.3 but yields an error under 7.1RC1 or RC2.

The error message is:
psql:outbug.sql:43: ERROR: Sub-SELECT uses un-GROUPed attribute
h.ordnum from outer query

Tom, you patched util/clauses.c (near line 540) a while back to prevent
the same error message on a different query. This may be related.

The SQL is a little strange because the subquery tries to reference
individual records from the outer query and then sum them.
The more I look at it, I wonder if it is not just bad SQL. But the last
one I found like this turned out to reveal a bug, so here it is:

drop table ord_hdr;
drop table cinv_hdr;
drop table cinv_items;
drop table inc_link;

create table ord_hdr (
ordnum int4,
proj int4
);

create table cinv_hdr (
ordnum int4,
hinum int4,
status varchar
);

create table cinv_items (
ordnum int4,
hinum int4,
quant int4,
unit_price numeric(12,2)
);

create table inc_link (
ordnum int4,
hinum int4,
amount numeric(12,2)
);

select sum(i.quant*i.unit_price::float8),
(select coalesce(sum(amount),0) from inc_link where ordnum = h.ordnum
and hinum = h.hinum)

from cinv_hdr h, cinv_items i, ord_hdr o where

o.ordnum = h.ordnum and
h.ordnum = i.ordnum and
h.hinum = i.hinum and

o.proj = 1051 and
h.status = 'open'
;