terrible STL set iterator behavior

wtfset.cpp

#include <set>
#include <iostream>

class A
{
    std::set<int> s;
public:
    A() { s.insert(0); s.insert(1); }

    std::set<int> getSet() { return s; }
};

int main(void)
{
    A a;
    std::cout << "A contains " << a.getSet().size() << " elements. They are listed below:" << std::endl;
    for (std::set<int>::const_iterator it = a.getSet().begin(); it != a.getSet().end(); ++it){
        std::cout << *it << std::endl;
    }
    return 0;
}

Expected output:

A contains 2 elements. They are listed below:
0
1

Actual output:

A contains 2 elements. They are listed below:
0
Segmentation fault: 11

The issue seems to be that I'm returning a set by value. However, that is the recommended style since STL containers are shallow copied. In the case of set, it seems that it causes weird behavior.