Alias of VALUES RTE in explain plan

Hi All,
While reviewing Richard's patch for grouping sets, I stumbled upon
following explain output

explain (costs off)
select distinct on (a, b) a, b
from (values (1, 1), (2, 2)) as t (a, b) where a = b
group by grouping sets((a, b), (a))
order by a, b;
QUERY PLAN
----------------------------------------------------------------
Unique
-> Sort
Sort Key: "*VALUES*".column1, "*VALUES*".column2
-> HashAggregate
Hash Key: "*VALUES*".column1, "*VALUES*".column2
Hash Key: "*VALUES*".column1
-> Values Scan on "*VALUES*"
Filter: (column1 = column2)
(8 rows)

There is no VALUES.column1 and VALUES.column2 in the query. The alias t.a
and t.b do not appear anywhere in the explain output. I think explain
output should look like
explain (costs off)
select distinct on (a, b) a, b
from (values (1, 1), (2, 2)) as t (a, b) where a = b
group by grouping sets((a, b), (a))
order by a, b;
QUERY PLAN
----------------------------------------------------------------
Unique
-> Sort
Sort Key: t.a, t.b
-> HashAggregate
Hash Key: t.a, t.b
Hash Key: t.a
-> Values Scan on "*VALUES*" t
Filter: (a = b)
(8 rows)

I didn't get time to figure out the reason behind this, nor the history.
But I thought I would report it nonetheless.

--
Best Wishes,
Ashutosh Bapat