ExecEvalExpr: unknown expression type 501 from coalesce

With 7.0.2, there seems to be another coalesce weirdness:

pjw=# create table tb(i int);
CREATE
pjw=# create table tbx(o int, n int);
CREATE
pjw=# update tb set i = coalesce((select n from tbx x where x.o = tb.i),tb.i);
UPDATE 0
pjw=# insert into tb values(1);
INSERT 1379795 1
pjw=# insert into tb values(2);
INSERT 1379796 1
pjw=# insert into tb values(0);
INSERT 1379797 1
pjw=# insert into tbx values(1,2);
INSERT 1379798 1
pjw=# insert into tbx values(2,1);
INSERT 1379799 1
pjw=# update tb set i = coalesce((select n from tbx x where x.o = tb.i),tb.i);
ERROR: ExecEvalExpr: unknown expression type 501

This seems to be fixed in current CVS but I'd be interested in a patch for
7.0.2, if there is one...

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