[foldr]

This could happen any time you return a pointer to a variable with automatic storage and then later attempt to dereference the pointer and do something with the value. Of course, you shouldn't do that, but the C++ compiler won't stop you. 'Scope' can have various meanings, but merely understanding how lexical scoping of variables works is not sufficient to understand why you shouldn't do that.

[zabzonk]

well, let me rephrase "scope" as "lifetime of objects"

[foldr]

Ok, but then what you're saying is almost tautological. Indeed, you won't be surprised when an object is destroyed in C++ if you understand how object lifetimes work in C++.