Optimizer bug in UPDATE with subselect

I've upgraded my DB to 7.3.1 from 7.2. The following update causes the SEQ
SCAN instead of INDEX SCAN (in 7.2 there was no bug like that):

create table machines(
i_sprzetx int,
mod char(10),
type char(30)
);

create table sprzetx(
rowid int,
ident char(50)
);

create index i_sprzetx on sprzetx(ident);

inserts....

vacuum analyze sprzetx;

update machines set i_sprzetx=(
select g.rowid from sprzetx g
where g.ident=( trim(f.type) || trim(f.mod) )
);

When optimizer meets ANY expression int the query clause switches from INDEX
to SEQUENTIAL disregarding the expression is constant for row.

Helps ALTER COLUMN to machines, UPDATE to TRIM || TRIM but sure it's not
solution.

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