Implicit conversion from int to enum class in switch statement

enum class pid
{
    Alpha, Beta, Gamma
};

int main()
{
    int propId = 2;
    switch(propId)
    {
    case pid::Alpha:
    case pid::Beta:
    case pid::Gamma:
        break;
    }
}

Above snippet compiles fine in msvc2012 (and works) but fails in clang-3.4 and g++-4.8. These require static_cast<pid>(propId) to be used inside switch clause.

Incidentally, simple assignment without explicit cast such as pid a = propId; gives error in each compiler.

Which one got it right?