Given this code fragment:

--------------
struct Bag(S...)
{
    alias S Types;
}

template Test(alias i, B)
{
    void fn() {
        foreach(t; B.Types)
        {
            switch(i) {
                case IndexOf!(t, B.Types):
                {
                    pragma(msg, __traits(allMembers, t));
                    pragma(msg, __traits(hasMember, t, "m"));
                    break;
                }
                default: {}
            }
        }
    }
}

struct A
{
    int m;
}


void main()
{

    int i;
    alias Test!(i, Bag!(A)).fn func;
}
----------------------

DMD will output:
----------------------
tuple("m")
false
---------------------

It seems that __traits(hasMember, ..) evaluates to false, despite the fact that the type 
does have a member "m". However if the template Test does not have an alias parameter, everything will work just fine.