Parameter pack causes "uninitialized local variable" in Visual Studio

The following code compiles well under gcc and clang, but throws the C4700 "uninitialized local variable 'a' used" error in Visual Studio:

template<size_t T>
class V
{
public:
    int v[T];

    V() = default;
    template<typename ...A>
    V(A... args):
        v{static_cast<T>(args)...}
    {}
};

int main()
{
    V<2> a(2, 2);
    V<2> b = a;
    return 0;
}

If I add body to the constructor (by removing the = default and adding {}) the error goes away. I can' t find anything that mandates this behavior in the spec. Is this a bug in Visual C++ compiler or I am missing something in the spec?