subquery q2 does not have attribute 0

In playing with a sample query from another thread I found this
query is broken on the master branch:

select q1.*
  from (select 'a'::text) q1(c)
  where not exists
   (select * from (select 'A'::text) q2(c) where q2 = q1);

I get:

ERROR:  subquery q2 does not have attribute 0

I checked and found it broken on 9.2 and 9.3, but working on 9.1.
git bisect, says it was broken by commit
1cb108efb0e60d87e4adec38e7636b6e8efbeb57.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company