`weak_ptr::expired` behavior in the dtor of the object

Consider the following code:

#include <iostream>
#include <memory>
using namespace std;

class T;

std::weak_ptr<T> wptr;

class T
{
public:
    T() {  }
    ~T() {
        std::cout << "in dtor" << std::endl;
        std::cout << (wptr.expired() ? "expired" : "not expired") << std::endl;
    }
};

int main() {
    {
        auto ptr = std::make_shared<T>();
        wptr = ptr;
        std::cout << (wptr.expired() ? "expired" : "not expired") << std::endl;
    }
    return 0;
}

In this code, I was trying to find out if weak_ptrs are expired in the objects destruction phase. It seems so. The output is:

not expired
in dtor
expired

I used gcc-5.1 with ideone.

Now, I have another problem. I couldn't find any documentation stating that this is the standard behavior. Is it guaranteed to work this way, always?