A set operation involving a nested view can result in expression symbols in the select clause of the first union branch which cause the alias generator logic to not work properly (as the expressions can collide) and place an unwanted projected symbol in the select clause of the source query. This could look something like:
select v_0.c_0 ... v_0.actualName ...
This can be reproduced with:
and issuing the query:
Note that the inner_view has two projected expressions with the same constant/null value.