copy elision visible side effect

Consider this code:

#include <iostream>

using namespace std;

struct Foo {
public:
    int _a{};
    Foo(int a) : _a{a} 
    {
        std::cout << "ctor" << std::endl;
    }

    Foo(const Foo &)
    {
        std::cout << "copy" << std::endl;
    }
};

int main () {
    Foo a{10};
    Foo b = 10;
    std::cout << b._a << std::endl;
}

When I compile with

g++ -std=c++11 -fno-elide-constructors test.cpp

the output is

ctor ctor copy 0

which is what I expect, since the in Foo b = 10, 10 is implicitly constructed from int, then b is copy constructed from Foo. Furthermore, my copy constructor doesn't do anything, so the member _a remains 0 (as it is in-class-initialized).

However, when I use copy elision

g++ -std=c++11 test.cpp

the output is

ctor ctor 10

which is surprising to say the least. I understand that the copy constructor is elided here, but this is a serious side-effect (the fact that the member is once initialized to 0 and once to 10), as it affects the rest of the code path.

Is this behaviour normal?