String switch is odd using betterC

[Abby via Digitalmars-d-learn]

I have a simple enum of strings like so:

enum Alphabet : string
{
    a = "A",
    b = "B",
    c = "C",
    d = "D",
    e = "E",
    f = "F",
    g = "G"
}
and then simple final switch like so:

extern(C) void main()
{
    auto s = Alphabet.f;
    final switch(s)
    {
        case Alphabet.a: break;
        case Alphabet.b: break;
        case Alphabet.c: break;
        case Alphabet.d: break;
        case Alphabet.e: break;
        case Alphabet.f: break;
        case Alphabet.g: break;
    }
}

The problem I have is that this causes:

/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(2999): 
Error: TypeInfo cannot be used with -betterC

Odd think is that wehen I remove g from my enum it compiles just 
fine, so it seems that this compilation error occurs only when my 
enum has more then 6 members.

Any idea why?