Is this temp table behaviour documented?

Question

Query Language (SQL) and PL/pgSQL functions treat temp tables differently:

begin;
create table foo(id) as values (1);
select * from foo;
/*
 id
----
  1
*/
savepoint s;
create function f() returns setof integer language sql as $$
  create temporary table foo(id) on commit drop as values (2);
  select id from foo;
$$;
select * from f();
/*
 f
---
 1
*/
rollback to s;
create function f() returns setof integer language plpgsql as $$
begin
  create temporary table foo(id) on commit drop as values (2);
  return query select id from foo;
end;
$$;
select * from f();
/*
 f
---
 2
*/
rollback;

The docs say:

...Existing permanent tables with the same name are not visible to the current session while the temporary table exists, unless they are referenced with schema-qualified names...

This does not mention the exception demonstrated above. Is this documented elsewhere?