Yes it is.  The comprehension is a *new* scope, within the outer scope of the exec, and it *cannot see* the variables in the outer scope of the exec.  You have the same problem if you try to use a comprehension in that way in a class statement at the class level.  An exec is explicitly *not* equivalent to a function body.  It is equivalent to operating in a class body, if you give it two namespaces, and in a global context if you give it one.  This is documented.

Please don't reopen the issue.