Is it safe to capture a member reference if the class storing the original reference goes out of scope?

Consider this:

#include <iostream>
#include <functional>

std::function<void()> task;
int x = 42;

struct Foo
{
   int& x;

   void bar()
   {
      task = [=]() { std::cout << x << '\n'; };
   }
};

int main()
{
   {
      Foo f{x};
      f.bar();
   }

   task();
}

My instinct was that, as the actual referent still exists when the task is executed, we get a newly-bound reference at the time the lambda is encountered and everything is fine.

However, on my GCC 4.8.5 (CentOS 7), I'm seeing some behaviour (in a more complex program) that suggests this is instead UB because f, and the reference f.x itself, have died. Is that right?