is this a known bug in 9.6?

Hi,

this is a stock PGDG 9.6:

postgres=# with i(x) as (values (1::int)), j(y) as (values (2::int)) select
x from (select x from i union all select y from j) b;
x
---
1
2
(2 rows)

postgres=# with i(x) as (values (1::int)), j(y) as (values (2::int)) select
max(x) from (select x from i union all select y from j) b;
ERROR: could not find plan for CTE "i"

The same on 9.5:

postgres=# with i(x) as (values (1::int)), j(y) as (values (2::int)) select
x from (select x from i union all select y from j) b;
x
---
1
2
(2 rows)

postgres=# with i(x) as (values (1::int)), j(y) as (values (2::int)) select
max(x) from (select x from i union all select y from j) b;
max
-----
2
(1 row)

Is this a bug or is my assumption that this should work wrong?

Both the aggregate and the UNION are required to trigger the bug:

postgres=# with i(x) as (values (1::int)) select x from (select x from i
union all select 3::int) b;
x
---
1
3
(2 rows)

postgres=# with i(x) as (values (1::int)) select max(x) from (select x from
i) b;
max
-----
1
(1 row)

postgres=# with i(x) as (values (1::int)) select max(x) from (select x from
i union all select 3::int) b;
ERROR: could not find plan for CTE "i"

Thanks,
Torsten