Victor, Pablo, I added you two since you commented on the duplicate.

I believe this should be closed as 'not a bug'.  The doc for globals() says is returns a 'dictionary', meaning an instance of dict.  The doc for exec says globals "must be a dictionary (and not a subclass of dictionary)".  (This is mere implied when locals is also given, but it *is* implied.).  The behavior when globals is otherwise is undefined.