Re: BUG #16212: subquery block allows to overwrite table aliasdefined earlier

These are just examples of poorly written queries where sub-query correlated value injection results in an arbitrary edge case: specifically, when a query can resolve a name as either a column or a table it chooses the column.  Your choice of encoding your expected and actual output doesn't help you here as you are not distinguishing between a scalar column result and a composite table result being present.

select a from (values(1)) a; -- yields (1); the parens denote the result is a composite with a single field (whose name is "column1" since it was not given a name explicitly)

select a from (values(1)) a (a); -- yields 1; no parens denote the scalar result of 1 since the column named "a" exists and is preferred over the table named "a"