function pointer bug?

[bitwise via Digitalmars-d]

I am trying to store a function pointer in a class in a generic 
way(works with all member/non-member/global functions).

In the main() function below, there are two cases(A, B).

If case B is commented out, this code complies/runs fine. 
Otherwise, I get these errors, and the compiler pointing at 
"dg.funcptr = &T[0];" in TestClas.invoke(void*).

Error: this for instanceMethod needs to be type TestClass not 
type main.FuncPtr!(instanceMethod).FuncPtr
Error: cannot implicitly convert expression 
(&(__error).instanceMethod) of type void delegate() to void 
function()
Error: template instance main.FuncPtr!(instanceMethod) error 
instantiating


Am I missing something here or is this a bug?

class TestClass {
     void instanceMethod() {
         writeln("Instance Method!");
     }

     static void staticMethod() {
         writeln("Static Method!");
     }
}

void GlobalMethod() {
     writeln("Global Method!");
}

void invokeFunction(T...)(void *instance){
     alias typeof(T[0])                       method_type;
     alias ReturnType!method_type             return_type;
     alias ParameterTypeTuple!method_type     param_types;
     alias return_type delegate(param_types)  delegate_type;

     delegate_type dg;
     dg.ptr = instance;
     dg.funcptr = &T[0];
     dg();
}

class FuncPtr(T...) {
     void invoke(void *instance) {
         alias typeof(T[0])                       method_type;
         alias ReturnType!method_type             return_type;
         alias ParameterTypeTuple!method_type     param_types;
         alias return_type delegate(param_types)  delegate_type;

         delegate_type dg;
         dg.ptr = instance;
         dg.funcptr = &T[0];
         dg();
     }
}

void main() {
     TestClass testClass = new TestClass();

     // case A
     
invokeFunction!(TestClass.instanceMethod)(cast(void*)testClass);
     invokeFunction!(TestClass.staticMethod)(null);
     invokeFunction!(GlobalMethod)(null);

     // case B
     auto fp1 = new FuncPtr!(TestClass.instanceMethod);
     auto fp2 = new FuncPtr!(TestClass.staticMethod);
     auto fp3 = new FuncPtr!(GlobalMethod);

     fp1.invoke(cast(void*)testClass);
     fp2.invoke(null);
     fp3.invoke(null);
}